Explicitly localize strings to Locale.US for internal implementation

There is inconsistent usage of toLowerCase/toUpperCase methods in the codebase.
Somewhere we already use Locale.US, somewhere not. That might cause various issues in runtime
as shown in CASSANDRA-19953 ticket when an environment Cassandra runs in has different locale from expected.
In this patch, all such method calls explicitly set their locale to Locale.US. This patch also contains
a checkstyle rule which fails the compilation if toLowerCase or toUpperCase is used.
We prefer calls to methods in LocalizeString class which use US locale.

patch by Ata İlhan Köktürk; reviewed by Stefan Miklosovic, Brandon Williams for CASSANDRA-19953

Co-authored-by: Maxwell Guo <cclive1601@gmail.com>
Co-authored-by: Stefan Miklosovic <smiklosovic@apacheorg>

.build/checkstyle.xml

@@ -62,7 +62,13 @@
       <property name="idFormat" value="blockPathToFile"/>
       <property name="influenceFormat" value="0"/>
     </module>
- 
+
+    <module name="SuppressWithNearbyCommentFilter">
+      <property name="commentFormat" value="checkstyle: permit this invocation"/>
+      <property name="idFormat" value="blockToCases"/>
+      <property name="influenceFormat" value="0"/>
+    </module>
+
     <module name="RegexpSinglelineJava">
       <!-- block system time -->
       <property name="id" value="blockSystemClock"/>
@@ -151,6 +157,14 @@
       <property name="message" value="Avoid Short() and use Short.valueOf()" />
     </module>
 
+    <module name="RegexpSinglelineJava">
+      <!-- block toLowerCase and toUpperCase -->
+      <property name="id" value="blockToCases"/>
+      <property name="format" value="toLowerCase\(|toUpperCase\("/>
+      <property name="ignoreComments" value="true"/>
+      <property name="message" value="Avoid toLowerCase() or toUpperCase() and use LocalizeString class instead" />
+    </module>
+
     <module name="SuppressionCommentFilter">
       <property name="offCommentFormat" value="checkstyle: suppress below '([\w\|]+)'"/>
       <property name="idFormat" value="$1"/>

CHANGES.txt

@@ -1,4 +1,5 @@
 5.1
+ * Explicitly localize strings to Locale.US for internal implementation (CASSANDRA-19953)
  * Add -H option for human-friendly output in nodetool compactionhistory (CASSANDRA-20015)
  * Fix type check for referenced duration type for nested types (CASSANDRA-19890)
  * In simulation tests, correctly set the tokens of replacement nodes (CASSANDRA-19997)

src/antlr/Cql.g

@@ -50,6 +50,7 @@ import Parser,Lexer;
     import org.apache.cassandra.exceptions.SyntaxException;
     import org.apache.cassandra.schema.ColumnMetadata;
     import org.apache.cassandra.utils.Pair;
+    import org.apache.cassandra.utils.LocalizeString;
 }
 
 @members {

src/antlr/Parser.g

@@ -722,7 +722,7 @@ createFunctionStatement returns [CreateFunctionStatement.Raw stmt]
       K_LANGUAGE language = IDENT
       K_AS body = STRING_LITERAL
       { $stmt = new CreateFunctionStatement.Raw(
-          fn, argNames, argTypes, returnType, calledOnNullInput, $language.text.toLowerCase(), $body.text, orReplace, ifNotExists);
+          fn, argNames, argTypes, returnType, calledOnNullInput, LocalizeString.toLowerCaseLocalized($language.text), $body.text, orReplace, ifNotExists);
       }
     ;
 
@@ -1127,7 +1127,7 @@ listPermissionsStatement returns [ListPermissionsStatement stmt]
 
 permission returns [Permission perm]
     : p=(K_CREATE | K_ALTER | K_DROP | K_SELECT | K_MODIFY | K_AUTHORIZE | K_DESCRIBE | K_EXECUTE | K_UNMASK | K_SELECT_MASKED)
-    { $perm = Permission.valueOf($p.text.toUpperCase()); }
+    { $perm = Permission.valueOf(LocalizeString.toUpperCaseLocalized($p.text)); }
     ;
 
 permissionOrAll returns [Set<Permission> perms]
@@ -1642,7 +1642,7 @@ functionName returns [FunctionName s]
     ;
 
 allowedFunctionName returns [String s]
-    : f=IDENT                       { $s = $f.text.toLowerCase(); }
+    : f=IDENT                       { $s = LocalizeString.toLowerCaseLocalized($f.text); }
     | f=QUOTED_NAME                 { $s = $f.text; }
     | u=unreserved_function_keyword { $s = u; }
     | K_TOKEN                       { $s = "token"; }

src/java/org/apache/cassandra/audit/AuditLogManager.java

@@ -51,6 +51,8 @@ import org.apache.cassandra.transport.messages.ResultMessage;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.MBeanWrapper;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Central location for managing the logging of client/user-initated actions (like queries, log in commands, and so on).
  *
@@ -387,7 +389,7 @@ public class AuditLogManager implements QueryEvents.Listener, AuthEvents.Listene
         {
             for (String query : queries)
             {
-                if (query.toLowerCase().contains(PasswordObfuscator.PASSWORD_TOKEN))
+                if (toLowerCaseLocalized(query).contains(PasswordObfuscator.PASSWORD_TOKEN))
                     return "Syntax Exception. Obscured for security reasons.";
             }
         }

src/java/org/apache/cassandra/audit/AuditLogOptions.java

@@ -34,6 +34,8 @@ import org.apache.cassandra.exceptions.ConfigurationException;
 import org.apache.cassandra.io.util.File;
 import org.apache.cassandra.utils.binlog.BinLogOptions;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public class AuditLogOptions extends BinLogOptions
 {
     public volatile boolean enabled = false;
@@ -143,13 +145,13 @@ public class AuditLogOptions extends BinLogOptions
 
         public Builder withIncludedCategories(final String includedCategories)
         {
-            sanitise(includedCategories).map(v -> this.includedCategories = v.toUpperCase());
+            sanitise(includedCategories).map(v -> this.includedCategories = toUpperCaseLocalized(v));
             return this;
         }
 
         public Builder withExcludedCategories(final String excludedCategories)
         {
-            sanitise(excludedCategories).map(v -> this.excludedCategories = v.toUpperCase());
+            sanitise(excludedCategories).map(v -> this.excludedCategories = toUpperCaseLocalized(v));
             return this;
         }
 
@@ -173,7 +175,7 @@ public class AuditLogOptions extends BinLogOptions
 
         public Builder withRollCycle(final String rollCycle)
         {
-            sanitise(rollCycle).map(v -> this.rollCycle = v.toUpperCase());
+            sanitise(rollCycle).map(v -> this.rollCycle = toUpperCaseLocalized(v));
             return this;
         }
 
@@ -230,8 +232,8 @@ public class AuditLogOptions extends BinLogOptions
             opts.logger = this.logger;
             sanitise(this.includedKeyspaces).map(v -> opts.included_keyspaces = v);
             sanitise(this.excludedKeyspaces).map(v -> opts.excluded_keyspaces = v);
-            sanitise(this.includedCategories).map(v -> opts.included_categories = v.toUpperCase());
+            sanitise(this.includedCategories).map(v -> opts.included_categories = toUpperCaseLocalized(v));
-            sanitise(this.excludedCategories).map(v -> opts.excluded_categories = v.toUpperCase());
+            sanitise(this.excludedCategories).map(v -> opts.excluded_categories = toUpperCaseLocalized(v));
             sanitise(this.includedUsers).map(v -> opts.included_users = v);
             sanitise(this.excludedUsers).map(v -> opts.excluded_users = v);
             opts.roll_cycle = this.rollCycle;

src/java/org/apache/cassandra/concurrent/Stage.java

@@ -39,6 +39,7 @@ import org.apache.cassandra.utils.concurrent.Future;
 
 import static java.util.stream.Collectors.toMap;
 import static org.apache.cassandra.concurrent.ExecutorFactory.Global.executorFactory;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public enum Stage
 {
@@ -79,7 +80,7 @@ public enum Stage
     private static String normalizeName(String stageName)
     {
         // Handle discrepancy between JMX names and actual pool names
-        String upperStageName = stageName.toUpperCase();
+        String upperStageName = toUpperCaseLocalized(stageName);
         if (upperStageName.endsWith("STAGE"))
         {
             upperStageName = upperStageName.substring(0, stageName.length() - 5);

src/java/org/apache/cassandra/config/CassandraRelevantProperties.java

@@ -32,6 +32,8 @@ import org.apache.cassandra.service.FileSystemOwnershipCheck;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.StorageCompatibilityMode;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 // checkstyle: suppress below 'blockSystemPropertyUsage'
 
 /** A class that extracts system properties for the cassandra node it runs within. */
@@ -918,7 +920,7 @@ public enum CassandraRelevantProperties
     }
 
     /**
-     * Gets the value of a system property as a enum, calling {@link String#toUpperCase()} first.
+     * Gets the value of a system property as an enum, calling {@link org.apache.cassandra.utils.LocalizeString#toUpperCaseLocalized(String)} first.
      *
      * @param defaultValue to return when not defined
      * @param <T> type
@@ -930,7 +932,7 @@ public enum CassandraRelevantProperties
     }
 
     /**
-     * Gets the value of a system property as a enum, optionally calling {@link String#toUpperCase()} first.
+     * Gets the value of a system property as an enum, optionally calling {@link org.apache.cassandra.utils.LocalizeString#toUpperCaseLocalized(String)} first.
      *
      * @param toUppercase before converting to enum
      * @param defaultValue to return when not defined
@@ -942,11 +944,11 @@ public enum CassandraRelevantProperties
         String value = System.getProperty(key);
         if (value == null)
             return defaultValue;
-        return Enum.valueOf(defaultValue.getDeclaringClass(), toUppercase ? value.toUpperCase() : value);
+        return Enum.valueOf(defaultValue.getDeclaringClass(), toUppercase ? toUpperCaseLocalized(value) : value);
     }
 
     /**
-     * Gets the value of a system property as an enum, optionally calling {@link String#toUpperCase()} first.
+     * Gets the value of a system property as an enum, optionally calling {@link org.apache.cassandra.utils.LocalizeString#toLowerCaseLocalized(String)} first.
      * If the value is missing, the default value for this property is used
      *
      * @param toUppercase before converting to enum
@@ -957,7 +959,7 @@ public enum CassandraRelevantProperties
     public <T extends Enum<T>> T getEnum(boolean toUppercase, Class<T> enumClass)
     {
         String value = System.getProperty(key, defaultVal);
-        return Enum.valueOf(enumClass, toUppercase ? value.toUpperCase() : value);
+        return Enum.valueOf(enumClass, toUppercase ? toUpperCaseLocalized(value) : value);
     }
 
     /**

src/java/org/apache/cassandra/config/DataRateSpec.java

@@ -27,6 +27,7 @@ import com.google.common.math.DoubleMath;
 import com.google.common.primitives.Ints;
 
 import static org.apache.cassandra.config.DataRateSpec.DataRateUnit.BYTES_PER_SECOND;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * Represents a data rate type used for cassandra configuration. It supports the opportunity for the users to be able to
@@ -76,7 +77,7 @@ public abstract class DataRateSpec
         // negatives are not allowed by the regex pattern
         if (minUnit.convert(quantity, unit) >= max)
             throw new IllegalArgumentException("Invalid data rate: " + value + ". It shouldn't be more than " +
-                                             (max - 1) + " in " + minUnit.name().toLowerCase());
+                                             (max - 1) + " in " + toLowerCaseLocalized(minUnit.name()));
     }
 
     private static void validateQuantity(double quantity, DataRateUnit unit, DataRateUnit minUnit, long max)
@@ -86,8 +87,8 @@ public abstract class DataRateSpec
 
         if (minUnit.convert(quantity, unit) >= max)
             throw new IllegalArgumentException(String.format("Invalid data rate: %s %s. It shouldn't be more than %d in %s",
-                                                       quantity, unit.name().toLowerCase(),
+                                                       quantity, toLowerCaseLocalized(unit.name()),
-                                                       max - 1, minUnit.name().toLowerCase()));
+                                                       max - 1, toLowerCaseLocalized(minUnit.name())));
     }
 
     // get vs no-get prefix is not consistent in the code base, but for classes involved with config parsing, it is

src/java/org/apache/cassandra/config/DataStorageSpec.java

@@ -28,6 +28,7 @@ import com.google.common.primitives.Ints;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.BYTES;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.KIBIBYTES;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.MEBIBYTES;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * Represents an amount of data storage. Wrapper class for Cassandra configuration parameters, providing to the
@@ -99,7 +100,7 @@ public abstract class DataStorageSpec
 
         if (minUnit.convert(quantity, sourceUnit) >= max)
             throw new IllegalArgumentException("Invalid data storage: " + value + ". It shouldn't be more than " +
-                                               (max - 1) + " in " + minUnit.name().toLowerCase());
+                                               (max - 1) + " in " + toLowerCaseLocalized(minUnit.name()));
     }
 
     private static void validateQuantity(long quantity, DataStorageUnit sourceUnit, DataStorageUnit minUnit, long max)
@@ -109,8 +110,8 @@ public abstract class DataStorageSpec
 
         if (minUnit.convert(quantity, sourceUnit) >= max)
             throw new IllegalArgumentException(String.format("Invalid data storage: %d %s. It shouldn't be more than %d in %s",
-                                                             quantity, sourceUnit.name().toLowerCase(),
+                                                             quantity, toLowerCaseLocalized(sourceUnit.name()),
-                                                             max - 1, minUnit.name().toLowerCase()));
+                                                             max - 1, toLowerCaseLocalized(minUnit.name())));
     }
 
     // get vs no-get prefix is not consistent in the code base, but for classes involved with config parsing, it is

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -62,7 +62,7 @@ import com.google.common.collect.Sets;
 import com.google.common.primitives.Ints;
 import com.google.common.primitives.Longs;
 import com.google.common.util.concurrent.RateLimiter;
-import org.apache.cassandra.utils.Pair;
+
 import org.apache.commons.lang3.ArrayUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.slf4j.Logger;
@@ -116,6 +116,7 @@ import org.apache.cassandra.service.StorageService;
 import org.apache.cassandra.service.paxos.Paxos;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.MBeanWrapper;
+import org.apache.cassandra.utils.Pair;
 import org.apache.cassandra.utils.StorageCompatibilityMode;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.ALLOCATE_TOKENS_FOR_KEYSPACE;
@@ -156,6 +157,7 @@ import static org.apache.cassandra.db.ConsistencyLevel.QUORUM;
 import static org.apache.cassandra.io.util.FileUtils.ONE_GIB;
 import static org.apache.cassandra.io.util.FileUtils.ONE_MIB;
 import static org.apache.cassandra.utils.Clock.Global.logInitializationOutcome;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public class DatabaseDescriptor
 {
@@ -1785,7 +1787,7 @@ public class DatabaseDescriptor
         if (cidrAuthorizerMode == null || cidrAuthorizerMode.isEmpty())
             return defaultCidrAuthorizerMode;
 
-        return ICIDRAuthorizer.CIDRAuthorizerMode.valueOf(cidrAuthorizerMode.toUpperCase());
+        return ICIDRAuthorizer.CIDRAuthorizerMode.valueOf(toUpperCaseLocalized(cidrAuthorizerMode));
     }
 
     public static int getCidrGroupsCacheRefreshInterval()

src/java/org/apache/cassandra/config/DurationSpec.java

@@ -34,6 +34,8 @@ import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Represents a positive time duration. Wrapper class for Cassandra duration configuration parameters, providing to the
  * users the opportunity to be able to provide config with a unit of their choice in cassandra.yaml as per the available
@@ -108,7 +110,7 @@ public abstract class DurationSpec
 
         if (minUnit.convert(quantity, sourceUnit) >= max)
             throw new IllegalArgumentException("Invalid duration: " + value + ". It shouldn't be more than " +
-                                             (max - 1) + " in " + minUnit.name().toLowerCase());
+                                             (max - 1) + " in " + toLowerCaseLocalized(minUnit.name()));
     }
 
     private static void validateQuantity(long quantity, TimeUnit sourceUnit, TimeUnit minUnit, long max)
@@ -118,8 +120,8 @@ public abstract class DurationSpec
 
         if (minUnit.convert(quantity, sourceUnit) >= max)
             throw new IllegalArgumentException(String.format("Invalid duration: %d %s. It shouldn't be more than %d in %s",
-                                                           quantity, sourceUnit.name().toLowerCase(),
+                                                           quantity, toLowerCaseLocalized(sourceUnit.name()),
-                                                           max - 1, minUnit.name().toLowerCase()));
+                                                           max - 1, toLowerCaseLocalized(minUnit.name())));
     }
 
     // get vs no-get prefix is not consistent in the code base, but for classes involved with config parsing, it is
@@ -141,7 +143,7 @@ public abstract class DurationSpec
      */
     static TimeUnit fromSymbol(String symbol)
     {
-        switch (symbol.toLowerCase())
+        switch (toLowerCaseLocalized(symbol))
         {
             case "d": return DAYS;
             case "h": return HOURS;

src/java/org/apache/cassandra/config/EncryptionOptions.java

@@ -38,6 +38,8 @@ import org.apache.cassandra.security.DisableSslContextFactory;
 import org.apache.cassandra.security.ISslContextFactory;
 import org.apache.cassandra.utils.FBUtilities;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * This holds various options used for enabling SSL/TLS encryption.
  * Examples of such options are: supported cipher-suites, ssl protocol with version, accepted protocols, end-point
@@ -78,7 +80,7 @@ public class EncryptionOptions
             for (ClientAuth clientAuth : ClientAuth.values())
             {
                 VALUES.put(clientAuth.value, clientAuth);
-                VALUES.put(clientAuth.name().toLowerCase(), clientAuth);
+                VALUES.put(toLowerCaseLocalized(clientAuth.name()), clientAuth);
             }
         }
 
@@ -89,9 +91,9 @@ public class EncryptionOptions
 
         public static ClientAuth from(String value)
         {
-            if (VALUES.containsKey(value.toLowerCase()))
+            if (VALUES.containsKey(toLowerCaseLocalized(value)))
             {
-                return VALUES.get(value.toLowerCase());
+                return VALUES.get(toLowerCaseLocalized(value));
             }
             throw new ConfigurationException(value + " is not a valid ClientAuth option");
         }
@@ -183,7 +185,7 @@ public class EncryptionOptions
             Set<String> valueSet = new HashSet<>();
             ConfigKey[] values = values();
             for(ConfigKey key: values) {
-                valueSet.add(key.getKeyName().toLowerCase());
+                valueSet.add(toLowerCaseLocalized(key.getKeyName()));
             }
             return valueSet;
         }
@@ -302,7 +304,7 @@ public class EncryptionOptions
             Set<String> configKeys = ConfigKey.asSet();
             for (Map.Entry<String, String> entry : ssl_context_factory.parameters.entrySet())
             {
-                if(configKeys.contains(entry.getKey().toLowerCase()))
+                if(configKeys.contains(toLowerCaseLocalized(entry.getKey())))
                 {
                     throw new IllegalArgumentException("SslContextFactory "+ssl_context_factory.class_name+" should " +
                                                        "configure '"+entry.getKey()+"' as encryption_options instead of" +

src/java/org/apache/cassandra/cql3/CQL3Type.java

@@ -42,6 +42,7 @@ import org.apache.cassandra.service.ClientState;
 import org.apache.cassandra.utils.ByteBufferUtil;
 
 import static java.util.stream.Collectors.toList;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public interface CQL3Type
 {
@@ -139,7 +140,7 @@ public interface CQL3Type
         @Override
         public String toString()
         {
-            return super.toString().toLowerCase();
+            return toLowerCaseLocalized(super.toString());
         }
     }
 

src/java/org/apache/cassandra/cql3/ColumnIdentifier.java

@@ -19,7 +19,6 @@ package org.apache.cassandra.cql3;
 
 import java.nio.ByteBuffer;
 import java.util.List;
-import java.util.Locale;
 import java.util.concurrent.ConcurrentMap;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -34,6 +33,8 @@ import org.apache.cassandra.utils.ByteBufferUtil;
 import org.apache.cassandra.utils.ObjectSizes;
 import org.apache.cassandra.utils.memory.ByteBufferCloner;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Represents an identifer for a CQL column definition.
  * TODO : should support light-weight mode without text representation for when not interned
@@ -109,7 +110,7 @@ public class ColumnIdentifier implements IMeasurableMemory, Comparable<ColumnIde
 
     public ColumnIdentifier(String rawText, boolean keepCase)
     {
-        this.text = keepCase ? rawText : rawText.toLowerCase(Locale.US);
+        this.text = keepCase ? rawText : toLowerCaseLocalized(rawText);
         this.bytes = ByteBufferUtil.bytes(this.text);
         this.prefixComparison = prefixComparison(bytes);
         this.interned = false;
@@ -140,7 +141,7 @@ public class ColumnIdentifier implements IMeasurableMemory, Comparable<ColumnIde
 
     public static ColumnIdentifier getInterned(String rawText, boolean keepCase)
     {
-        String text = keepCase ? rawText : rawText.toLowerCase(Locale.US);
+        String text = keepCase ? rawText : toLowerCaseLocalized(rawText);
         ByteBuffer bytes = ByteBufferUtil.bytes(text);
         return getInterned(UTF8Type.instance, bytes, text);
     }

src/java/org/apache/cassandra/cql3/Duration.java

@@ -30,6 +30,7 @@ import org.apache.cassandra.serializers.MarshalException;
 import static org.apache.cassandra.cql3.statements.RequestValidations.checkFalse;
 import static org.apache.cassandra.cql3.statements.RequestValidations.checkTrue;
 import static org.apache.cassandra.cql3.statements.RequestValidations.invalidRequest;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.apache.commons.lang3.time.DateUtils.MILLIS_PER_DAY;
 
 import io.netty.util.concurrent.FastThreadLocal;
@@ -251,7 +252,7 @@ public final class Duration
 
     private static Builder add(Builder builder, long number, String symbol)
     {
-        switch (symbol.toLowerCase())
+        switch (toLowerCaseLocalized(symbol))
         {
             case "y": return builder.addYears(number);
             case "mo": return builder.addMonths(number);

src/java/org/apache/cassandra/cql3/FieldIdentifier.java

@@ -17,13 +17,14 @@
  */
 package org.apache.cassandra.cql3;
 
-import java.util.Locale;
 import java.nio.ByteBuffer;
 
 import org.apache.cassandra.db.marshal.UTF8Type;
 import org.apache.cassandra.exceptions.SyntaxException;
 import org.apache.cassandra.serializers.MarshalException;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Identifies a field in a UDT.
  */
@@ -41,7 +42,7 @@ public class FieldIdentifier
      */
     public static FieldIdentifier forUnquoted(String text)
     {
-        return new FieldIdentifier(convert(text == null ? null : text.toLowerCase(Locale.US)));
+        return new FieldIdentifier(convert(text == null ? null : toLowerCaseLocalized(text)));
     }
 
     /**

src/java/org/apache/cassandra/cql3/PasswordObfuscator.java

@@ -23,13 +23,15 @@ import java.util.Optional;
 import org.apache.cassandra.auth.PasswordAuthenticator;
 import org.apache.cassandra.auth.RoleOptions;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Obfuscates passwords in a given string
  */
 public class PasswordObfuscator
 {
     public static final String OBFUSCATION_TOKEN = "*******";
-    public static final String PASSWORD_TOKEN = PasswordAuthenticator.PASSWORD_KEY.toLowerCase();
+    public static final String PASSWORD_TOKEN = toLowerCaseLocalized(PasswordAuthenticator.PASSWORD_KEY);
 
     /**
      * Obfuscates everything after the first appearance password token
@@ -42,7 +44,7 @@ public class PasswordObfuscator
         if (null == sourceString)
             return null;
 
-        int passwordTokenStartIndex = sourceString.toLowerCase().indexOf(PASSWORD_TOKEN);
+        int passwordTokenStartIndex = toLowerCaseLocalized(sourceString).indexOf(PASSWORD_TOKEN);
         if (passwordTokenStartIndex < 0)
             return sourceString;
 

src/java/org/apache/cassandra/cql3/QualifiedName.java

@@ -17,9 +17,10 @@
  */
 package org.apache.cassandra.cql3;
 
-import java.util.Locale;
 import java.util.Objects;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Class for the names of the keyspace-prefixed elements (e.g. table, index, view names)
  */
@@ -123,6 +124,6 @@ public class QualifiedName
      */
     private static String toInternalName(String name, boolean keepCase)
     {
-        return keepCase ? name : name.toLowerCase(Locale.US);
+        return keepCase ? name : toLowerCaseLocalized(name);
     }
 }

src/java/org/apache/cassandra/cql3/ReservedKeywords.java

@@ -30,6 +30,8 @@ import com.google.common.collect.ImmutableSet;
 
 import org.apache.cassandra.exceptions.ConfigurationException;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public final class ReservedKeywords
 {
     private static final String FILE_NAME = "reserved_keywords.txt";
@@ -58,6 +60,6 @@ public final class ReservedKeywords
 
     public static boolean isReserved(String text)
     {
-        return reservedKeywords.contains(text.toUpperCase());
+        return reservedKeywords.contains(toUpperCaseLocalized(text));
     }
 }

src/java/org/apache/cassandra/cql3/RoleName.java

@@ -17,7 +17,7 @@
  */
 package org.apache.cassandra.cql3;
 
-import java.util.Locale;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public class RoleName
 {
@@ -25,7 +25,7 @@ public class RoleName
 
     public void setName(String name, boolean keepCase)
     {
-        this.name = keepCase ? name : (name == null ? name : name.toLowerCase(Locale.US));
+        this.name = keepCase ? name : (name == null ? name : toLowerCaseLocalized(name));
     }
 
     public boolean hasName()

src/java/org/apache/cassandra/cql3/SchemaElement.java

@@ -18,7 +18,8 @@
 package org.apache.cassandra.cql3;
 
 import java.util.Comparator;
-import java.util.Locale;
+
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * A schema element (keyspace, udt, udf, uda, table, index, view).
@@ -43,7 +44,7 @@ public interface SchemaElement
         @Override
         public String toString()
         {
-            return super.toString().toLowerCase(Locale.US);
+            return toLowerCaseLocalized(super.toString());
         }
     }
 

src/java/org/apache/cassandra/cql3/functions/CastFcts.java

@@ -45,6 +45,7 @@ import org.apache.cassandra.db.marshal.UUIDType;
 import org.apache.cassandra.transport.ProtocolVersion;
 
 import static org.apache.cassandra.cql3.functions.TimeFcts.*;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 import org.apache.commons.lang3.StringUtils;
 
@@ -196,7 +197,7 @@ public final class CastFcts
 
     private static String toLowerCaseString(CQL3Type type)
     {
-        return type.toString().toLowerCase();
+        return toLowerCaseLocalized(type.toString());
     }
 
     /**

src/java/org/apache/cassandra/cql3/functions/FunctionResolver.java

@@ -35,6 +35,7 @@ import org.apache.cassandra.schema.UserFunctions;
 
 import static java.util.stream.Collectors.joining;
 import static org.apache.cassandra.cql3.statements.RequestValidations.invalidRequest;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public final class FunctionResolver
 {
@@ -46,7 +47,7 @@ public final class FunctionResolver
     {
         return new ColumnSpecification(receiverKeyspace,
                                        receiverTable,
-                                       new ColumnIdentifier("arg" + i + '(' + fun.name().toString().toLowerCase() + ')', true),
+                                       new ColumnIdentifier("arg" + i + '(' + toLowerCaseLocalized(fun.name().toString()) + ')', true),
                                        fun.argTypes().get(i));
     }
 

src/java/org/apache/cassandra/cql3/functions/masking/MaskingFunction.java

@@ -26,6 +26,8 @@ import org.apache.cassandra.cql3.functions.FunctionParameter;
 import org.apache.cassandra.cql3.functions.NativeScalarFunction;
 import org.apache.cassandra.db.marshal.AbstractType;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * A {@link NativeScalarFunction} that totally or partially replaces the original value of a column value,
  * meant to obscure the real value of the column.
@@ -56,7 +58,7 @@ public abstract class MaskingFunction extends NativeScalarFunction
     {
         public Factory(String name, FunctionParameter... parameters)
         {
-            super(NAME_PREFIX + name.toLowerCase(), parameters);
+            super(NAME_PREFIX + toLowerCaseLocalized(name), parameters);
         }
     }
 }

src/java/org/apache/cassandra/cql3/functions/types/DataType.java

@@ -23,6 +23,8 @@ import com.google.common.collect.ImmutableList;
 
 import org.apache.cassandra.transport.ProtocolVersion;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Data types supported by cassandra.
  */
@@ -122,7 +124,7 @@ public abstract class DataType
         @Override
         public String toString()
         {
-            return super.toString().toLowerCase();
+            return toLowerCaseLocalized(super.toString());
         }
     }
 

src/java/org/apache/cassandra/cql3/functions/types/Duration.java

@@ -23,6 +23,7 @@ import java.util.regex.Pattern;
 import com.google.common.base.Objects;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * Represents a duration. A duration stores separately months, days, and seconds due to the fact
@@ -237,7 +238,7 @@ public final class Duration
 
     private static Builder add(Builder builder, long number, String symbol)
     {
-        String s = symbol.toLowerCase();
+        String s = toLowerCaseLocalized(symbol);
         if (s.equals("y"))
         {
             return builder.addYears(number);

src/java/org/apache/cassandra/cql3/functions/types/Metadata.java

@@ -19,6 +19,8 @@ package org.apache.cassandra.cql3.functions.types;
 
 import org.apache.cassandra.cql3.ColumnIdentifier;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Keeps metadata on the connected cluster, including known nodes and schema definitions.
  */
@@ -65,7 +67,7 @@ public class Metadata
         }
         if (isAlphanumeric)
         {
-            return id.toLowerCase();
+            return toLowerCaseLocalized(id);
         }
 
         // Check if it's enclosed in quotes. If it is, remove them and unescape internal double quotes

src/java/org/apache/cassandra/cql3/selection/Selectable.java

@@ -42,6 +42,7 @@ import org.apache.cassandra.utils.Pair;
 
 import static org.apache.cassandra.cql3.selection.SelectorFactories.createFactoriesAndCollectColumnDefinitions;
 import static org.apache.cassandra.cql3.statements.RequestValidations.invalidRequest;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public interface Selectable extends AssignmentTestable
 {
@@ -447,7 +448,7 @@ public interface Selectable extends AssignmentTestable
         @Override
         public String toString()
         {
-            return String.format("cast(%s as %s)", arg, type.toString().toLowerCase());
+            return String.format("cast(%s as %s)", arg, toLowerCaseLocalized(type.toString()));
         }
 
         public Selector.Factory newSelectorFactory(TableMetadata table, AbstractType<?> expectedType, List<ColumnMetadata> defs, VariableSpecifications boundNames)

src/java/org/apache/cassandra/cql3/selection/Selection.java

@@ -37,6 +37,8 @@ import org.apache.cassandra.schema.TableMetadata;
 import org.apache.cassandra.transport.ProtocolVersion;
 import org.apache.cassandra.utils.JsonUtils;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public abstract class Selection
 {
     /**
@@ -327,7 +329,7 @@ public abstract class Selection
                 sb.append(", ");
 
             String columnName = spec.name.toString();
-            if (!columnName.equals(columnName.toLowerCase(Locale.US)))
+            if (!columnName.equals(toLowerCaseLocalized(columnName)))
                 columnName = "\"" + columnName + "\"";
 
             sb.append('"');

src/java/org/apache/cassandra/cql3/statements/PropertyDefinitions.java

@@ -28,6 +28,7 @@ import org.slf4j.LoggerFactory;
 import org.apache.cassandra.exceptions.SyntaxException;
 
 import static java.lang.String.format;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public class PropertyDefinitions
 {
@@ -113,7 +114,7 @@ public class PropertyDefinitions
         if (null == value)
             throw new IllegalArgumentException("value argument can't be null");
 
-        String lowerCasedValue = value.toLowerCase();
+        String lowerCasedValue = toLowerCaseLocalized(value);
 
         if (POSITIVE_PATTERN.matcher(lowerCasedValue).matches())
             return true;

src/java/org/apache/cassandra/db/ConsistencyLevel.java

@@ -17,9 +17,6 @@
  */
 package org.apache.cassandra.db;
 
-
-import java.util.Locale;
-
 import com.carrotsearch.hppc.ObjectIntHashMap;
 import org.apache.cassandra.locator.Endpoints;
 import org.apache.cassandra.locator.InOurDc;
@@ -31,6 +28,7 @@ import org.apache.cassandra.locator.NetworkTopologyStrategy;
 import org.apache.cassandra.transport.ProtocolException;
 
 import static org.apache.cassandra.locator.Replicas.addToCountPerDc;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public enum ConsistencyLevel
 {
@@ -85,7 +83,7 @@ public enum ConsistencyLevel
 
     public static ConsistencyLevel fromString(String str)
     {
-        return valueOf(str.toUpperCase(Locale.US));
+        return valueOf(toUpperCaseLocalized(str));
     }
 
     public static int quorumFor(AbstractReplicationStrategy replicationStrategy)

src/java/org/apache/cassandra/db/Directories.java

@@ -79,6 +79,8 @@ import org.apache.cassandra.utils.DirectorySizeCalculator;
 import org.apache.cassandra.utils.JVMStabilityInspector;
 import org.apache.cassandra.utils.Pair;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * Encapsulate handling of paths to the data files.
  *
@@ -755,11 +757,11 @@ public class Directories
      */
     public static boolean isStoredInLocalSystemKeyspacesDataLocation(String keyspace, String table)
     {
-        String keyspaceName = keyspace.toLowerCase();
+        String keyspaceName = toLowerCaseLocalized(keyspace);
 
         return SchemaConstants.LOCAL_SYSTEM_KEYSPACE_NAMES.contains(keyspaceName)
                 && !(SchemaConstants.SYSTEM_KEYSPACE_NAME.equals(keyspaceName)
-                        && SystemKeyspace.TABLES_SPLIT_ACROSS_MULTIPLE_DISKS.contains(table.toLowerCase()));
+                        && SystemKeyspace.TABLES_SPLIT_ACROSS_MULTIPLE_DISKS.contains(toLowerCaseLocalized(table)));
     }
 
     public static class DataDirectory

src/java/org/apache/cassandra/db/compaction/OperationType.java

@@ -17,6 +17,8 @@
  */
 package org.apache.cassandra.db.compaction;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public enum OperationType
 {
     /** Each modification here should be also applied to {@link org.apache.cassandra.tools.nodetool.Stop#compactionType} */
@@ -69,7 +71,7 @@ public enum OperationType
     OperationType(String type, boolean writesData, int priority)
     {
         this.type = type;
-        this.fileName = type.toLowerCase().replace(" ", "");
+        this.fileName = toLowerCaseLocalized(type).replace(" ", "");
         this.writesData = writesData;
         this.priority = priority;
     }

src/java/org/apache/cassandra/db/compaction/unified/Controller.java

@@ -25,18 +25,19 @@ import java.util.Random;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
 
-import org.apache.cassandra.config.CassandraRelevantProperties;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import org.apache.cassandra.config.DatabaseDescriptor;
+import org.apache.cassandra.config.CassandraRelevantProperties;
 import org.apache.cassandra.db.ColumnFamilyStore;
 import org.apache.cassandra.db.compaction.UnifiedCompactionStrategy;
 import org.apache.cassandra.exceptions.ConfigurationException;
-import org.apache.cassandra.utils.Overlaps;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.MonotonicClock;
+import org.apache.cassandra.utils.Overlaps;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 /**
 * The controller provides compaction parameters to the unified compaction strategy
 */
@@ -442,7 +443,7 @@ public class Controller
             sstableGrowthModifier = FBUtilities.parsePercent(options.get(SSTABLE_GROWTH_OPTION));
 
         Overlaps.InclusionMethod inclusionMethod = options.containsKey(OVERLAP_INCLUSION_METHOD_OPTION)
-                ? Overlaps.InclusionMethod.valueOf(options.get(OVERLAP_INCLUSION_METHOD_OPTION).toUpperCase())
+                ? Overlaps.InclusionMethod.valueOf(toUpperCaseLocalized(options.get(OVERLAP_INCLUSION_METHOD_OPTION)))
                 : DEFAULT_OVERLAP_INCLUSION_METHOD;
 
         return new Controller(cfs,
@@ -583,7 +584,7 @@ public class Controller
         {
             try
             {
-                Overlaps.InclusionMethod.valueOf(s.toUpperCase());
+                Overlaps.InclusionMethod.valueOf(toUpperCaseLocalized(s));
             }
             catch (IllegalArgumentException e)
             {

src/java/org/apache/cassandra/db/lifecycle/LogRecord.java

@@ -46,6 +46,8 @@ import org.apache.cassandra.io.util.FileUtils;
 import org.apache.cassandra.io.util.PathUtils;
 import org.apache.cassandra.utils.FBUtilities;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 /**
  * A decoded line in a transaction log file replica.
  *
@@ -63,7 +65,7 @@ final class LogRecord
 
         public static Type fromPrefix(String prefix)
         {
-            return valueOf(prefix.toUpperCase());
+            return valueOf(toUpperCaseLocalized(prefix));
         }
 
         public boolean hasFile()

src/java/org/apache/cassandra/db/marshal/CollectionType.java

@@ -25,7 +25,6 @@ import java.util.List;
 import java.util.Iterator;
 import java.util.Objects;
 import java.util.function.Consumer;
-import java.util.Locale;
 
 import org.apache.cassandra.cql3.CQL3Type;
 import org.apache.cassandra.cql3.ColumnSpecification;
@@ -46,6 +45,8 @@ import org.apache.cassandra.utils.bytecomparable.ByteComparable;
 import org.apache.cassandra.utils.bytecomparable.ByteSource;
 import org.apache.cassandra.utils.bytecomparable.ByteSourceInverse;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * The abstract validator that is the base for maps, sets and lists (both frozen and non-frozen).
  *
@@ -85,7 +86,7 @@ public abstract class CollectionType<T> extends MultiElementType<T>
         @Override
         public String toString()
         {
-            return super.toString().toLowerCase(Locale.US);
+            return toLowerCaseLocalized(super.toString());
         }
     }
 
@@ -142,7 +143,7 @@ public abstract class CollectionType<T> extends MultiElementType<T>
     public <V> void validate(V value, ValueAccessor<V> accessor) throws MarshalException
     {
         if (accessor.isEmpty(value))
-            throw new MarshalException("Not enough bytes to read a " + kind.name().toLowerCase());
+            throw new MarshalException("Not enough bytes to read a " + toLowerCaseLocalized(kind.name()));
         super.validate(value, accessor);
     }
 

src/java/org/apache/cassandra/db/marshal/EmptyType.java

@@ -39,6 +39,7 @@ import org.apache.cassandra.utils.bytecomparable.ByteSource;
 import org.apache.cassandra.utils.NoSpamLogger;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.SERIALIZATION_EMPTY_TYPE_NONEMPTY_BEHAVIOR;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 /**
  * A type that only accept empty data.
@@ -59,7 +60,7 @@ public class EmptyType extends AbstractType<Void>
             return NonEmptyWriteBehavior.FAIL;
         try
         {
-            return NonEmptyWriteBehavior.valueOf(value.toUpperCase().trim());
+            return NonEmptyWriteBehavior.valueOf(toUpperCaseLocalized(value).trim());
         }
         catch (Exception e)
         {

src/java/org/apache/cassandra/db/marshal/UserType.java

@@ -50,6 +50,7 @@ import static com.google.common.collect.Iterables.any;
 import static com.google.common.collect.Iterables.transform;
 import static org.apache.cassandra.config.CassandraRelevantProperties.TYPE_UDT_CONFLICT_BEHAVIOR;
 import static org.apache.cassandra.cql3.ColumnIdentifier.maybeQuote;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * A user defined type.
@@ -274,7 +275,7 @@ public class UserType extends TupleType implements SchemaElement
                 sb.append(", ");
 
             String name = stringFieldNames.get(i);
-            if (!name.equals(name.toLowerCase(Locale.US)))
+            if (!name.equals(toLowerCaseLocalized(name)))
                 name = "\"" + name + "\"";
 
             sb.append('"');

src/java/org/apache/cassandra/db/virtual/ClientsTable.java

@@ -32,6 +32,8 @@ import org.apache.cassandra.metrics.ClientMetrics;
 import org.apache.cassandra.schema.TableMetadata;
 import org.apache.cassandra.transport.ConnectedClient;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 final class ClientsTable extends AbstractVirtualTable
 {
     private static final String ADDRESS = "address";
@@ -88,7 +90,7 @@ final class ClientsTable extends AbstractVirtualTable
             result.row(remoteAddress.getAddress(), remoteAddress.getPort())
                   .column(HOSTNAME, remoteAddress.getHostName())
                   .column(USERNAME, client.username().orElse(null))
-                  .column(CONNECTION_STAGE, client.stage().toString().toLowerCase())
+                  .column(CONNECTION_STAGE, toLowerCaseLocalized(client.stage().toString()))
                   .column(PROTOCOL_VERSION, client.protocolVersion())
                   .column(CLIENT_OPTIONS, client.clientOptions().orElse(null))
                   .column(DRIVER_NAME, client.driverName().orElse(null))

src/java/org/apache/cassandra/db/virtual/CollectionVirtualTableAdapter.java

@@ -85,6 +85,7 @@ import org.apache.cassandra.utils.Pair;
 
 import static org.apache.cassandra.db.rows.Cell.NO_DELETION_TIME;
 import static org.apache.cassandra.utils.FBUtilities.camelToSnake;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * This is a virtual table that iteratively builds rows using a data set provided by internal collection.
@@ -255,7 +256,7 @@ public class CollectionVirtualTableAdapter<R> implements VirtualTable
         Pattern pattern = Pattern.compile("^[A-Z1-9_]+$");
         // Contains only uppercase letters, numbers and underscores, so it's already snake case.
         if (pattern.matcher(camel).matches())
-            return camel.toLowerCase();
+            return toLowerCaseLocalized(camel);
 
         // Some special cases must be handled manually.
         String modifiedCamel = camel;

src/java/org/apache/cassandra/db/virtual/GossipInfoTable.java

@@ -35,6 +35,7 @@ import org.apache.cassandra.locator.InetAddressAndPort;
 import org.apache.cassandra.schema.TableMetadata;
 
 import static org.apache.cassandra.gms.ApplicationState.TOKENS;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * A {@link VirtualTable} that return the Gossip information in tabular format.
@@ -101,10 +102,10 @@ final class GossipInfoTable extends AbstractVirtualTable
                                           .column(HEARTBEAT, getHeartBeat(localState));
 
             for (ApplicationState state : STATES_FOR_VALUES)
-                dataSet.column(state.name().toLowerCase(), getValue(localState, state));
+                dataSet.column(toLowerCaseLocalized(state.name()), getValue(localState, state));
 
             for (ApplicationState state : STATES_FOR_VERSIONS)
-                dataSet.column(state.name().toLowerCase() + "_version", getVersion(localState, state));
+                dataSet.column(toLowerCaseLocalized(state.name()) + "_version", getVersion(localState, state));
         }
         return result;
     }
@@ -178,10 +179,10 @@ final class GossipInfoTable extends AbstractVirtualTable
                                                      .addRegularColumn(HEARTBEAT, Int32Type.instance);
 
         for (ApplicationState state : STATES_FOR_VALUES)
-            builder.addRegularColumn(state.name().toLowerCase(), UTF8Type.instance);
+            builder.addRegularColumn(toLowerCaseLocalized(state.name()), UTF8Type.instance);
 
         for (ApplicationState state : STATES_FOR_VERSIONS)
-            builder.addRegularColumn(state.name().toLowerCase() + "_version", Int32Type.instance);
+            builder.addRegularColumn(toLowerCaseLocalized(state.name()) + "_version", Int32Type.instance);
 
         return builder.build();
     }

src/java/org/apache/cassandra/db/virtual/LocalRepairTables.java

@@ -49,6 +49,8 @@ import org.apache.cassandra.schema.TableMetadata;
 import org.apache.cassandra.service.ActiveRepairService;
 import org.apache.cassandra.utils.TimeUUID;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class LocalRepairTables
 {
     private LocalRepairTables()
@@ -385,7 +387,7 @@ public class LocalRepairTables
 
     private static String timestampColumnName(Enum<?> e)
     {
-        return timestampColumnName(e.name().toLowerCase());
+        return timestampColumnName(toLowerCaseLocalized(e.name()));
     }
 
     private static String timestampColumnName(String e)
@@ -431,7 +433,7 @@ public class LocalRepairTables
 
         T currentState = state.getStatus();
         State.Result result = state.getResult();
-        ds.column("status", result != null ? result.kind.name().toLowerCase() : currentState == null ? "init" : currentState.name().toLowerCase());
+        ds.column("status", result != null ? toLowerCaseLocalized(result.kind.name()) : currentState == null ? "init" : toLowerCaseLocalized(currentState.name()));
         for (Map.Entry<T, Long> e : state.getStateTimesMillis().entrySet())
         {
             if (e.getValue().longValue() != 0)

src/java/org/apache/cassandra/db/virtual/SSTableTasksTable.java

@@ -27,6 +27,8 @@ import org.apache.cassandra.db.marshal.UTF8Type;
 import org.apache.cassandra.dht.LocalPartitioner;
 import org.apache.cassandra.schema.TableMetadata;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 final class SSTableTasksTable extends AbstractVirtualTable
 {
     private final static String KEYSPACE_NAME = "keyspace_name";
@@ -74,11 +76,11 @@ final class SSTableTasksTable extends AbstractVirtualTable
                        task.getTable().orElse("*"),
                        task.getTaskId())
                   .column(COMPLETION_RATIO, completionRatio)
-                  .column(KIND, task.getTaskType().toString().toLowerCase())
+                  .column(KIND, toLowerCaseLocalized(task.getTaskType().toString()))
                   .column(PROGRESS, completed)
                   .column(SSTABLES, task.getSSTables().size())
                   .column(TOTAL, total)
-                  .column(UNIT, task.getUnit().toString().toLowerCase())
+                  .column(UNIT, toLowerCaseLocalized(task.getUnit().toString()))
                   .column(TARGET_DIRECTORY, task.targetDirectory());
         }
 

src/java/org/apache/cassandra/db/virtual/StreamingVirtualTable.java

@@ -28,6 +28,8 @@ import org.apache.cassandra.streaming.StreamManager;
 import org.apache.cassandra.streaming.StreamingState;
 import org.apache.cassandra.utils.TimeUUID;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 import static org.apache.cassandra.cql3.statements.schema.CreateTableStatement.parse;
 
 public class StreamingVirtualTable extends AbstractVirtualTable
@@ -60,7 +62,7 @@ public class StreamingVirtualTable extends AbstractVirtualTable
     {
         StringBuilder sb = new StringBuilder();
         for (StreamingState.Status state : StreamingState.Status.values())
-            sb.append("  status_").append(state.name().toLowerCase()).append("_timestamp timestamp,\n");
+            sb.append("  status_").append(toLowerCaseLocalized(state.name())).append("_timestamp timestamp,\n");
         return sb.toString();
     }
 
@@ -91,13 +93,13 @@ public class StreamingVirtualTable extends AbstractVirtualTable
         ds.column("follower", state.follower());
         ds.column("operation", state.operation().getDescription());
         ds.column("peers", state.peers().stream().map(Object::toString).collect(Collectors.toList()));
-        ds.column("status", state.status().name().toLowerCase());
+        ds.column("status", toLowerCaseLocalized(state.status().name()));
         ds.column("progress_percentage", round(state.progress() * 100));
         ds.column("duration_millis", state.durationMillis());
         ds.column("failure_cause", state.failureCause());
         ds.column("success_message", state.successMessage());
         for (Map.Entry<StreamingState.Status, Long> e : state.stateTimesMillis().entrySet())
-            ds.column("status_" + e.getKey().name().toLowerCase() + "_timestamp", new Date(e.getValue()));
+            ds.column("status_" + toLowerCaseLocalized(e.getKey().name()) + "_timestamp", new Date(e.getValue()));
 
         state.sessions().update(ds);
     }

src/java/org/apache/cassandra/db/virtual/VirtualSchemaKeyspace.java

@@ -29,6 +29,7 @@ import org.apache.cassandra.schema.TableMetadata;
 
 import static org.apache.cassandra.schema.SchemaConstants.VIRTUAL_SCHEMA;
 import static org.apache.cassandra.schema.TableMetadata.builder;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public final class VirtualSchemaKeyspace extends VirtualKeyspace
 {
@@ -136,9 +137,9 @@ public final class VirtualSchemaKeyspace extends VirtualKeyspace
                     for (ColumnMetadata column : table.columns())
                     {
                         result.row(column.ksName, column.cfName, column.name.toString())
-                              .column(CLUSTERING_ORDER, column.clusteringOrder().toString().toLowerCase())
+                              .column(CLUSTERING_ORDER, toLowerCaseLocalized(column.clusteringOrder().toString()))
                               .column(COLUMN_NAME_BYTES, column.name.bytes)
-                              .column(KIND, column.kind.toString().toLowerCase())
+                              .column(KIND, toLowerCaseLocalized(column.kind.toString()))
                               .column(POSITION, column.position())
                               .column(TYPE, column.type.asCQL3Type().toString());
                     }

src/java/org/apache/cassandra/index/sai/analyzer/filter/BasicFilters.java

@@ -23,6 +23,8 @@ import java.util.Locale;
 
 import org.apache.lucene.analysis.miscellaneous.ASCIIFoldingFilter;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class BasicFilters
 {
     private static final Locale DEFAULT_LOCALE = Locale.getDefault();
@@ -39,7 +41,7 @@ public class BasicFilters
         @Override
         public String process(String input)
         {
-            return input.toLowerCase(locale);
+            return toLowerCaseLocalized(input, locale);
         }
     }
 

src/java/org/apache/cassandra/index/sai/disk/v1/IndexWriterConfig.java

@@ -28,6 +28,7 @@ import org.apache.cassandra.index.sai.disk.v1.vector.OptimizeFor;
 import org.apache.cassandra.index.sai.utils.IndexTermType;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.SAI_VECTOR_SEARCH_MAX_TOP_K;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 /**
  * Per-index config for storage-attached index writers.
@@ -151,7 +152,7 @@ public class IndexWriterConfig
             }
             if (options.containsKey(SIMILARITY_FUNCTION))
             {
-                String option = options.get(SIMILARITY_FUNCTION).toUpperCase();
+                String option = toUpperCaseLocalized(options.get(SIMILARITY_FUNCTION));
                 try
                 {
                     similarityFunction = VectorSimilarityFunction.valueOf(option);
@@ -164,7 +165,7 @@ public class IndexWriterConfig
             }
             if (options.containsKey(OPTIMIZE_FOR))
             {
-                String option = options.get(OPTIMIZE_FOR).toUpperCase();
+                String option = toUpperCaseLocalized(options.get(OPTIMIZE_FOR));
                 try
                 {
                     optimizeFor = OptimizeFor.valueOf(option);

src/java/org/apache/cassandra/index/sai/disk/v1/vector/OptimizeFor.java

@@ -21,6 +21,7 @@ package org.apache.cassandra.index.sai.disk.v1.vector;
 import java.util.function.Function;
 
 import static java.lang.Math.pow;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 /**
  * Allows the vector index searches to be optimised for latency or recall. This is used by the
@@ -47,6 +48,6 @@ public enum OptimizeFor
 
     public static OptimizeFor fromString(String value)
     {
-        return valueOf(value.toUpperCase());
+        return valueOf(toUpperCaseLocalized(value));
     }
 }

src/java/org/apache/cassandra/index/sasi/analyzer/filter/BasicResultFilters.java

@@ -19,6 +19,9 @@ package org.apache.cassandra.index.sasi.analyzer.filter;
 
 import java.util.Locale;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 /**
  * Basic/General Token Filters
  */
@@ -42,7 +45,7 @@ public class BasicResultFilters
 
         public String process(String input) throws Exception
         {
-            return input.toLowerCase(locale);
+            return toLowerCaseLocalized(input, locale);
         }
     }
 
@@ -62,7 +65,7 @@ public class BasicResultFilters
 
         public String process(String input) throws Exception
         {
-            return input.toUpperCase(locale);
+            return toUpperCaseLocalized(input, locale);
         }
     }
 

src/java/org/apache/cassandra/index/sasi/disk/OnDiskIndexBuilder.java

@@ -43,6 +43,8 @@ import com.google.common.annotations.VisibleForTesting;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public class OnDiskIndexBuilder
 {
     private static final Logger logger = LoggerFactory.getLogger(OnDiskIndexBuilder.class);
@@ -62,7 +64,7 @@ public class OnDiskIndexBuilder
 
         public static Mode mode(String mode)
         {
-            return Mode.valueOf(mode.toUpperCase());
+            return Mode.valueOf(toUpperCaseLocalized(mode));
         }
 
         public boolean supports(Op op)

src/java/org/apache/cassandra/metrics/CassandraMetricsRegistry.java

@@ -22,7 +22,6 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
-import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -74,6 +73,7 @@ import static java.util.Optional.ofNullable;
 import static org.apache.cassandra.db.virtual.CollectionVirtualTableAdapter.createSinglePartitionedKeyFiltered;
 import static org.apache.cassandra.db.virtual.CollectionVirtualTableAdapter.createSinglePartitionedValueFiltered;
 import static org.apache.cassandra.schema.SchemaConstants.VIRTUAL_METRICS;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * Dropwizard metrics registry extension for Cassandra, as of for now uses the latest version of Dropwizard metrics
@@ -810,7 +810,7 @@ public class CassandraMetricsRegistry extends MetricRegistry
 
         private String calculateRateUnit(TimeUnit unit)
         {
-            final String s = unit.toString().toLowerCase(Locale.US);
+            final String s = toLowerCaseLocalized(unit.toString());
             return s.substring(0, s.length() - 1);
         }
     }
@@ -861,7 +861,7 @@ public class CassandraMetricsRegistry extends MetricRegistry
         {
             super(metric, objectName, rateUnit);
             this.metric = metric;
-            this.durationUnit = durationUnit.toString().toLowerCase(Locale.US);
+            this.durationUnit = toLowerCaseLocalized(durationUnit.toString());
         }
 
         @Override

src/java/org/apache/cassandra/schema/CQLTypeParser.java

@@ -24,6 +24,8 @@ import org.apache.cassandra.db.marshal.AbstractType;
 import org.apache.cassandra.db.marshal.UserType;
 
 import static org.apache.cassandra.utils.ByteBufferUtil.bytes;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public final class CQLTypeParser
 {
@@ -33,17 +35,17 @@ public final class CQLTypeParser
     {
         ImmutableSet.Builder<String> builder = ImmutableSet.builder();
         for (CQL3Type.Native primitive : CQL3Type.Native.values())
-            builder.add(primitive.name().toLowerCase());
+            builder.add(toLowerCaseLocalized(primitive.name()));
         PRIMITIVE_TYPES = builder.build();
     }
 
     public static AbstractType<?> parse(String keyspace, String unparsed, Types userTypes)
     {
-        String lowercased = unparsed.toLowerCase();
+        String lowercased = toLowerCaseLocalized(unparsed);
 
         // fast path for the common case of a primitive type
         if (PRIMITIVE_TYPES.contains(lowercased))
-            return CQL3Type.Native.valueOf(unparsed.toUpperCase()).getType();
+            return CQL3Type.Native.valueOf(toUpperCaseLocalized(unparsed)).getType();
 
         // special-case top-level UDTs
         UserType udt = userTypes.getNullable(bytes(lowercased));

src/java/org/apache/cassandra/schema/CachingParams.java

@@ -28,6 +28,7 @@ import org.apache.commons.lang3.StringUtils;
 import org.apache.cassandra.exceptions.ConfigurationException;
 
 import static java.lang.String.format;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 // CQL: {'keys' : 'ALL'|'NONE', 'rows_per_partition': '200'|'NONE'|'ALL'}
 public final class CachingParams
@@ -40,7 +41,7 @@ public final class CachingParams
         @Override
         public String toString()
         {
-            return name().toLowerCase();
+            return toLowerCaseLocalized(name());
         }
     }
 

src/java/org/apache/cassandra/schema/CompactionParams.java

@@ -42,6 +42,8 @@ import org.apache.cassandra.utils.FBUtilities;
 
 import static java.lang.String.format;
 import static org.apache.cassandra.config.CassandraRelevantProperties.DEFAULT_PROVIDE_OVERLAPPING_TOMBSTONES;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public final class CompactionParams
 {
@@ -58,7 +60,7 @@ public final class CompactionParams
         @Override
         public String toString()
         {
-            return name().toLowerCase();
+            return toLowerCaseLocalized(name());
         }
     }
 
@@ -123,8 +125,8 @@ public final class CompactionParams
         boolean isEnabled = options.containsKey(Option.ENABLED.toString())
                           ? Boolean.parseBoolean(options.get(Option.ENABLED.toString()))
                           : DEFAULT_ENABLED;
-        String overlappingTombstoneParm = options.getOrDefault(Option.PROVIDE_OVERLAPPING_TOMBSTONES.toString(),
+        String overlappingTombstoneParm = toUpperCaseLocalized(options.getOrDefault(Option.PROVIDE_OVERLAPPING_TOMBSTONES.toString(),
-                                                               DEFAULT_PROVIDE_OVERLAPPING_TOMBSTONES_PROPERTY_VALUE.toString()).toUpperCase();
+                                                               DEFAULT_PROVIDE_OVERLAPPING_TOMBSTONES_PROPERTY_VALUE.toString()));
         Optional<TombstoneOption> tombstoneOptional = TombstoneOption.forName(overlappingTombstoneParm);
         if (!tombstoneOptional.isPresent())
         {

src/java/org/apache/cassandra/schema/IndexMetadata.java

@@ -49,6 +49,7 @@ import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.UUIDSerializer;
 
 import static org.apache.cassandra.db.TypeSizes.sizeof;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * An immutable representation of secondary index metadata.
@@ -72,7 +73,7 @@ public final class IndexMetadata
     static
     {
         indexNameAliases.put(StorageAttachedIndex.NAME, StorageAttachedIndex.class.getCanonicalName());
-        indexNameAliases.put(StorageAttachedIndex.class.getSimpleName().toLowerCase(), StorageAttachedIndex.class.getCanonicalName());
+        indexNameAliases.put(toLowerCaseLocalized(StorageAttachedIndex.class.getSimpleName()), StorageAttachedIndex.class.getCanonicalName());
         indexNameAliases.put(SASIIndex.class.getSimpleName(), SASIIndex.class.getCanonicalName());
     }
 
@@ -159,7 +160,7 @@ public final class IndexMetadata
         if (isCustom())
         {
             String className = options.get(IndexTarget.CUSTOM_INDEX_OPTION_NAME);
-            return indexNameAliases.getOrDefault(className.toLowerCase(), className);
+            return indexNameAliases.getOrDefault(toLowerCaseLocalized(className), className);
         }
         return CassandraIndex.class.getName();
     }

src/java/org/apache/cassandra/schema/KeyspaceParams.java

@@ -32,6 +32,8 @@ import org.apache.cassandra.tcm.ClusterMetadata;
 import org.apache.cassandra.tcm.serialization.MetadataSerializer;
 import org.apache.cassandra.tcm.serialization.Version;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * An immutable class representing keyspace parameters (durability and replication).
  */
@@ -57,7 +59,7 @@ public final class KeyspaceParams
         @Override
         public String toString()
         {
-            return name().toLowerCase();
+            return toLowerCaseLocalized(name());
         }
     }
 

src/java/org/apache/cassandra/schema/SchemaConstants.java

@@ -32,6 +32,8 @@ import org.apache.cassandra.db.Digest;
 import org.apache.cassandra.db.SystemKeyspace;
 import org.apache.cassandra.tracing.TraceKeyspace;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * When adding new String keyspace names here, double check if it needs to be added to PartitionDenylist.canDenylistKeyspace
  */
@@ -93,7 +95,7 @@ public final class SchemaConstants
      */
     public static boolean isLocalSystemKeyspace(String keyspaceName)
     {
-        return LOCAL_SYSTEM_KEYSPACE_NAMES.contains(keyspaceName.toLowerCase()) || isVirtualSystemKeyspace(keyspaceName);
+        return LOCAL_SYSTEM_KEYSPACE_NAMES.contains(toLowerCaseLocalized(keyspaceName)) || isVirtualSystemKeyspace(keyspaceName);
     }
 
     /**
@@ -101,7 +103,7 @@ public final class SchemaConstants
      */
     public static boolean isReplicatedSystemKeyspace(String keyspaceName)
     {
-        return REPLICATED_SYSTEM_KEYSPACE_NAMES.contains(keyspaceName.toLowerCase());
+        return REPLICATED_SYSTEM_KEYSPACE_NAMES.contains(toLowerCaseLocalized(keyspaceName));
     }
 
     /**
@@ -110,7 +112,7 @@ public final class SchemaConstants
      */
     public static boolean isVirtualSystemKeyspace(String keyspaceName)
     {
-        return VIRTUAL_SYSTEM_KEYSPACE_NAMES.contains(keyspaceName.toLowerCase());
+        return VIRTUAL_SYSTEM_KEYSPACE_NAMES.contains(toLowerCaseLocalized(keyspaceName));
     }
 
     /**

src/java/org/apache/cassandra/schema/SchemaKeyspace.java

@@ -27,7 +27,7 @@ import javax.annotation.concurrent.NotThreadSafe;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.*;
-import com.google.common.collect.Maps;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -62,6 +62,8 @@ import static org.apache.cassandra.config.CassandraRelevantProperties.TEST_FLUSH
 import static org.apache.cassandra.cql3.QueryProcessor.executeInternal;
 import static org.apache.cassandra.cql3.QueryProcessor.executeOnceInternal;
 import static org.apache.cassandra.schema.SchemaKeyspaceTables.*;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 import static org.apache.cassandra.utils.Simulate.With.GLOBAL_CLOCK;
 
 /**
@@ -694,9 +696,9 @@ public final class SchemaKeyspace
         builder.update(Columns)
                .row(table.name, column.name.toString())
                .add("column_name_bytes", column.name.bytes)
-               .add("kind", column.kind.toString().toLowerCase())
+               .add("kind", toLowerCaseLocalized(column.kind.toString()))
                .add("position", column.position())
-               .add("clustering_order", column.clusteringOrder().toString().toLowerCase())
+               .add("clustering_order", toLowerCaseLocalized(column.clusteringOrder().toString()))
                .add("type", type.asCQL3Type().toString());
 
         ColumnMask mask = column.getMask();
@@ -758,7 +760,7 @@ public final class SchemaKeyspace
                .row(table.name, column.column.name.toString())
                .add("dropped_time", new Date(TimeUnit.MICROSECONDS.toMillis(column.droppedTime)))
                .add("type", column.column.type.asCQL3Type().toString())
-               .add("kind", column.column.kind.toString().toLowerCase());
+               .add("kind", toLowerCaseLocalized(column.column.kind.toString()));
     }
 
     private static void dropDroppedColumnFromSchemaMutation(TableMetadata table, DroppedColumn column, Mutation.SimpleBuilder builder)
@@ -1075,10 +1077,10 @@ public final class SchemaKeyspace
         String keyspace = row.getString("keyspace_name");
         String table = row.getString("table_name");
 
-        ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(row.getString("kind").toUpperCase());
+        ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(toUpperCaseLocalized(row.getString("kind")));
 
         int position = row.getInt("position");
-        ClusteringOrder order = ClusteringOrder.valueOf(row.getString("clustering_order").toUpperCase());
+        ClusteringOrder order = ClusteringOrder.valueOf(toUpperCaseLocalized(row.getString("clustering_order")));
 
         AbstractType<?> type = CQLTypeParser.parse(keyspace, row.getString("type"), types);
         if (order == ClusteringOrder.DESC)
@@ -1159,7 +1161,7 @@ public final class SchemaKeyspace
          */
         AbstractType<?> type = CQLTypeParser.parse(keyspace, row.getString("type"), org.apache.cassandra.schema.Types.none());
         ColumnMetadata.Kind kind = row.has("kind")
-                                 ? ColumnMetadata.Kind.valueOf(row.getString("kind").toUpperCase())
+                                 ? ColumnMetadata.Kind.valueOf(toUpperCaseLocalized(row.getString("kind")))
                                  : ColumnMetadata.Kind.REGULAR;
         assert kind == ColumnMetadata.Kind.REGULAR || kind == ColumnMetadata.Kind.STATIC
             : "Unexpected dropped column kind: " + kind;

src/java/org/apache/cassandra/schema/TableParams.java

@@ -44,6 +44,7 @@ import static java.lang.String.format;
 import static java.util.stream.Collectors.toMap;
 import static org.apache.cassandra.schema.TableParams.Option.*;
 import static org.apache.cassandra.db.TypeSizes.sizeof;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public final class TableParams
 {
@@ -73,7 +74,7 @@ public final class TableParams
         @Override
         public String toString()
         {
-            return name().toLowerCase();
+            return toLowerCaseLocalized(name());
         }
     }
 

src/java/org/apache/cassandra/security/JKSKeyProvider.java

@@ -29,6 +29,8 @@ import org.slf4j.LoggerFactory;
 import org.apache.cassandra.config.TransparentDataEncryptionOptions;
 import org.apache.cassandra.io.util.File;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * A {@code KeyProvider} that retrieves keys from a java keystore.
  */
@@ -64,7 +66,7 @@ public class JKSKeyProvider implements KeyProvider
     {
         // there's a lovely behavior with jceks files that all aliases are lower-cased
         if (isJceks)
-            keyAlias = keyAlias.toLowerCase();
+            keyAlias = toLowerCaseLocalized(keyAlias);
 
         Key key;
         try

src/java/org/apache/cassandra/security/SSLFactory.java

@@ -48,6 +48,7 @@ import org.apache.cassandra.security.ISslContextFactory.SocketType;
 import static org.apache.cassandra.config.CassandraRelevantProperties.DISABLE_TCACTIVE_OPENSSL;
 
 import static org.apache.cassandra.config.EncryptionOptions.ClientAuth.REQUIRED;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * A Factory for providing and setting up client {@link SSLSocket}s. Also provides
@@ -337,7 +338,7 @@ public final class SSLFactory
                     if (settingDescription != null)
                     {
                         logger.warn("Dropping unsupported cipher_suite {} from {} configuration",
-                                    c, settingDescription.toLowerCase());
+                                    c, toLowerCaseLocalized(settingDescription));
                     }
                 }
             }

src/java/org/apache/cassandra/serializers/CollectionSerializer.java

@@ -23,7 +23,6 @@ import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
-import java.util.Locale;
 import java.util.function.Consumer;
 
 import com.google.common.collect.Range;
@@ -34,6 +33,8 @@ import org.apache.cassandra.db.marshal.ValueAccessor;
 import org.apache.cassandra.db.marshal.AbstractType;
 import org.apache.cassandra.utils.ByteBufferUtil;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public abstract class CollectionSerializer<T> extends TypeSerializer<T>
 {
     protected abstract List<ByteBuffer> serializeValues(T value);
@@ -110,7 +111,7 @@ public abstract class CollectionSerializer<T> extends TypeSerializer<T>
      */
     private String getCollectionName()
     {
-        return getType().getSimpleName().toLowerCase(Locale.US);
+        return toLowerCaseLocalized(getType().getSimpleName());
     }
 
     /**

src/java/org/apache/cassandra/service/StartupChecks.java

@@ -80,6 +80,7 @@ import static org.apache.cassandra.config.CassandraRelevantProperties.IGNORE_KER
 import static org.apache.cassandra.config.CassandraRelevantProperties.JAVA_VERSION;
 import static org.apache.cassandra.config.CassandraRelevantProperties.JAVA_VM_NAME;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * Verifies that the system and environment is in a fit state to be started.
@@ -217,7 +218,7 @@ public class StartupChecks
             {
                 try
                 {
-                    if (affectedFileSystemTypes.contains(Files.getFileStore(path).type().toLowerCase()))
+                    if (affectedFileSystemTypes.contains(toLowerCaseLocalized(Files.getFileStore(path).type())))
                         affectedPaths.add(path);
                 }
                 catch (IOException e)

src/java/org/apache/cassandra/service/StorageProxy.java

@@ -177,6 +177,7 @@ import static org.apache.cassandra.service.paxos.v1.PrepareVerbHandler.doPrepare
 import static org.apache.cassandra.service.paxos.v1.ProposeVerbHandler.doPropose;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
 import static org.apache.cassandra.utils.Clock.Global.nanoTime;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 import static org.apache.cassandra.utils.TimeUUID.Generator.nextTimeUUID;
 import static org.apache.cassandra.utils.concurrent.CountDownLatch.newCountDownLatch;
 import static org.apache.commons.lang3.StringUtils.join;
@@ -2835,7 +2836,7 @@ public class StorageProxy implements StorageProxyMBean
     public String setIdealConsistencyLevel(String cl)
     {
         ConsistencyLevel original = DatabaseDescriptor.getIdealConsistencyLevel();
-        ConsistencyLevel newCL = ConsistencyLevel.valueOf(cl.trim().toUpperCase());
+        ConsistencyLevel newCL = ConsistencyLevel.valueOf(toUpperCaseLocalized(cl.trim()));
         DatabaseDescriptor.setIdealConsistencyLevel(newCL);
         return String.format("Updating ideal consistency level new value: %s old value %s", newCL, original.toString());
     }

src/java/org/apache/cassandra/service/paxos/ContentionStrategy.java

@@ -52,6 +52,7 @@ import static org.apache.cassandra.metrics.ClientRequestsMetricsHolder.casReadMe
 import static org.apache.cassandra.metrics.ClientRequestsMetricsHolder.casWriteMetrics;
 import static org.apache.cassandra.utils.Clock.Global.nanoTime;
 import static org.apache.cassandra.utils.Clock.waitUntil;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * <p>A strategy for making back-off decisions for Paxos operations that fail to make progress because of other paxos operations.
@@ -369,7 +370,7 @@ public class ContentionStrategy
         Type(String traceTitle)
         {
             this.traceTitle = traceTitle;
-            this.lowercase = name().toLowerCase();
+            this.lowercase = toLowerCaseLocalized(name());
         }
     }
 

src/java/org/apache/cassandra/service/reads/HybridSpeculativeRetryPolicy.java

@@ -27,6 +27,8 @@ import org.apache.cassandra.exceptions.ConfigurationException;
 import org.apache.cassandra.metrics.SnapshottingTimer;
 import org.apache.cassandra.schema.TableParams;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public class HybridSpeculativeRetryPolicy implements SpeculativeRetryPolicy
 {
     private static final Pattern PATTERN =
@@ -128,7 +130,7 @@ public class HybridSpeculativeRetryPolicy implements SpeculativeRetryPolicy
         SpeculativeRetryPolicy policy1 = value1 instanceof PercentileSpeculativeRetryPolicy ? value1 : value2;
         SpeculativeRetryPolicy policy2 = value1 instanceof FixedSpeculativeRetryPolicy ? value1 : value2;
 
-        Function function = Function.valueOf(matcher.group("fun").toUpperCase());
+        Function function = Function.valueOf(toUpperCaseLocalized(matcher.group("fun")));
         return new HybridSpeculativeRetryPolicy((PercentileSpeculativeRetryPolicy) policy1, (FixedSpeculativeRetryPolicy) policy2, function);
     }
 

src/java/org/apache/cassandra/service/reads/repair/ReadRepairStrategy.java

@@ -23,6 +23,8 @@ import org.apache.cassandra.locator.Endpoints;
 import org.apache.cassandra.locator.ReplicaPlan;
 import org.apache.cassandra.transport.Dispatcher;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public enum ReadRepairStrategy implements ReadRepair.Factory
 {
     NONE
@@ -45,6 +47,6 @@ public enum ReadRepairStrategy implements ReadRepair.Factory
 
     public static ReadRepairStrategy fromString(String s)
     {
-        return valueOf(s.toUpperCase());
+        return valueOf(toUpperCaseLocalized(s));
     }
 }

src/java/org/apache/cassandra/streaming/StreamResultFuture.java

@@ -36,6 +36,7 @@ import org.apache.cassandra.utils.FBUtilities;
 
 import static org.apache.cassandra.streaming.StreamingChannel.Factory.Global.streamingFactory;
 import static org.apache.cassandra.utils.Clock.Global.nanoTime;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 /**
  * A future on the result ({@link StreamState}) of a streaming plan.
@@ -198,7 +199,7 @@ public final class StreamResultFuture extends AsyncFuture<StreamState>
 
     void handleSessionComplete(StreamSession session)
     {
-        logger.info("[Stream #{}] Session with {} is {}", session.planId(), session.peer, session.state().name().toLowerCase());
+        logger.info("[Stream #{}] Session with {} is {}", session.planId(), session.peer, toLowerCaseLocalized(session.state().name()));
         fireStreamEvent(new StreamEvent.SessionCompleteEvent(session));
         SessionInfo sessionInfo = session.getSessionInfo();
         coordinator.addSessionInfo(sessionInfo);

src/java/org/apache/cassandra/streaming/StreamingState.java

@@ -42,6 +42,7 @@ import org.apache.cassandra.utils.Clock;
 import org.apache.cassandra.utils.ObjectSizes;
 import org.apache.cassandra.utils.TimeUUID;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.apache.cassandra.utils.TimeUUID.Generator.nextTimeUUID;
 
 public class StreamingState implements StreamEventHandler, IMeasurableMemory
@@ -214,14 +215,14 @@ public class StreamingState implements StreamEventHandler, IMeasurableMemory
     {
         TableBuilder table = new TableBuilder();
         table.add("id", id.toString());
-        table.add("status", status().name().toLowerCase());
+        table.add("status", toLowerCaseLocalized(status().name()));
         table.add("progress", (progress() * 100) + "%");
         table.add("duration_ms", Long.toString(durationMillis()));
         table.add("last_updated_ms", Long.toString(lastUpdatedAtMillis()));
         table.add("failure_cause", failureCause());
         table.add("success_message", successMessage());
         for (Map.Entry<Status, Long> e : stateTimesMillis().entrySet())
-            table.add("status_" + e.getKey().name().toLowerCase() + "_ms", e.toString());
+            table.add("status_" + toLowerCaseLocalized(e.getKey().name()) + "_ms", e.toString());
         return table.toString();
     }
 

src/java/org/apache/cassandra/tcm/MetadataKeys.java

@@ -29,9 +29,11 @@ import com.google.common.collect.ImmutableSet;
 import org.apache.cassandra.tcm.extensions.ExtensionKey;
 import org.apache.cassandra.tcm.extensions.ExtensionValue;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class MetadataKeys
 {
-    public static final String CORE_NS = MetadataKeys.class.getPackage().getName().toLowerCase(Locale.ROOT);
+    public static final String CORE_NS = toLowerCaseLocalized(MetadataKeys.class.getPackage().getName(), Locale.ROOT);
 
     public static final MetadataKey SCHEMA                  = make(CORE_NS, "schema", "dist_schema");
     public static final MetadataKey NODE_DIRECTORY          = make(CORE_NS, "membership", "node_directory");

src/java/org/apache/cassandra/tools/RepairRunner.java

@@ -23,6 +23,7 @@ import java.text.SimpleDateFormat;
 import java.util.List;
 import java.util.Map;
 
+import org.apache.cassandra.service.ActiveRepairService.ParentRepairStatus;
 import org.apache.cassandra.service.StorageServiceMBean;
 import org.apache.cassandra.utils.concurrent.Condition;
 
@@ -32,10 +33,10 @@ import org.apache.cassandra.utils.progress.jmx.JMXNotificationProgressListener;
 
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
 import static java.util.concurrent.TimeUnit.SECONDS;
-import static org.apache.cassandra.service.ActiveRepairService.ParentRepairStatus;
 import static org.apache.cassandra.service.ActiveRepairService.ParentRepairStatus.FAILED;
 import static org.apache.cassandra.service.ActiveRepairService.ParentRepairStatus.valueOf;
 import static org.apache.cassandra.tools.NodeProbe.JMX_NOTIFICATION_POLL_INTERVAL_SECONDS;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.apache.cassandra.utils.concurrent.Condition.newOneTimeCondition;
 import static org.apache.cassandra.utils.progress.ProgressEventType.*;
 
@@ -165,7 +166,7 @@ public class RepairRunner extends JMXNotificationProgressListener
                 case FAILED:
                     printMessage(String.format("%s %s discovered repair %s.",
                                               triggeringCondition,
-                                              queriedString, parentRepairStatus.name().toLowerCase()));
+                                              queriedString, toLowerCaseLocalized(parentRepairStatus.name())));
                     if (parentRepairStatus == FAILED)
                     {
                         error = new IOException(messages.get(0));

src/java/org/apache/cassandra/tools/StandaloneScrubber.java

@@ -58,6 +58,8 @@ import org.apache.cassandra.utils.Pair;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.TEST_UTIL_ALLOW_TOOL_REINIT_FOR_TEST;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public class StandaloneScrubber
 {
@@ -241,12 +243,12 @@ public class StandaloneScrubber
 
             static HeaderFixMode fromCommandLine(String value)
             {
-                return valueOf(value.replace('-', '_').toUpperCase().trim());
+                return valueOf(toUpperCaseLocalized(value.replace('-', '_')).trim());
             }
 
             String asCommandLineOption()
             {
-                return name().toLowerCase().replace('_', '-');
+                return toLowerCaseLocalized(name()).replace('_', '-');
             }
         }
 

src/java/org/apache/cassandra/tools/nodetool/ProfileLoad.java

@@ -41,6 +41,7 @@ import org.apache.cassandra.utils.Pair;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 import static org.apache.commons.lang3.StringUtils.join;
 
 @Command(name = "profileload", description = "Low footprint profiling of activity for a period of time")
@@ -113,7 +114,7 @@ public class ProfileLoad extends NodeToolCmd
         Set<String> available = Arrays.stream(SamplerType.values()).map(Enum::toString).collect(Collectors.toSet());
         for (String s : samplers.split(","))
         {
-            String sampler = s.trim().toUpperCase();
+            String sampler = toUpperCaseLocalized(s.trim());
             checkArgument(available.contains(sampler), String.format("'%s' sampler is not available from: %s", s, Arrays.toString(SamplerType.values())));
             targets.add(sampler);
         }

src/java/org/apache/cassandra/transport/CBUtil.java

@@ -47,6 +47,7 @@ import org.apache.cassandra.utils.UUIDGen;
 import org.apache.cassandra.utils.memory.MemoryUtil;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.CASSANDRA_NETTY_USE_HEAP_ALLOCATOR;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 /**
  * ByteBuf utility methods.
@@ -285,7 +286,7 @@ public abstract class CBUtil
         String value = CBUtil.readString(cb);
         try
         {
-            return Enum.valueOf(enumType, value.toUpperCase());
+            return Enum.valueOf(enumType, toUpperCaseLocalized(value));
         }
         catch (IllegalArgumentException e)
         {
@@ -399,7 +400,7 @@ public abstract class CBUtil
         Map<String, List<String>> m = new HashMap<String, List<String>>(length);
         for (int i = 0; i < length; i++)
         {
-            String k = readString(cb).toUpperCase();
+            String k = toUpperCaseLocalized(readString(cb));
             List<String> v = readStringList(cb);
             m.put(k, v);
         }

src/java/org/apache/cassandra/transport/Client.java

@@ -38,6 +38,9 @@ import org.apache.cassandra.utils.Hex;
 import org.apache.cassandra.utils.JVMStabilityInspector;
 import org.apache.cassandra.utils.MD5Digest;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public class Client extends SimpleClient
 {
     private final SimpleEventHandler eventHandler = new SimpleEventHandler();
@@ -100,7 +103,7 @@ public class Client extends SimpleClient
         Iterator<String> iter = splitter.split(line).iterator();
         if (!iter.hasNext())
             return null;
-        String msgType = iter.next().toUpperCase();
+        String msgType = toUpperCaseLocalized(iter.next());
         if (msgType.equals("STARTUP"))
         {
             Map<String, String> options = new HashMap<String, String>();
@@ -108,17 +111,17 @@ public class Client extends SimpleClient
             while (iter.hasNext())
             {
                String next = iter.next();
-               if (next.toLowerCase().equals("snappy"))
+               if (toLowerCaseLocalized(next).equals("snappy"))
                {
                    options.put(StartupMessage.COMPRESSION, "snappy");
                    connection.setCompressor(Compressor.SnappyCompressor.instance);
                }
-               if (next.toLowerCase().equals("lz4"))
+               if (toLowerCaseLocalized(next).equals("lz4"))
                {
                    options.put(StartupMessage.COMPRESSION, "lz4");
                    connection.setCompressor(Compressor.LZ4Compressor.instance);
                }
-               if (next.toLowerCase().equals("throw_on_overload"))
+               if (toLowerCaseLocalized(next).equals("throw_on_overload"))
                {
                    options.put(StartupMessage.THROW_ON_OVERLOAD, "1");
                    connection.setThrowOnOverload(true);
@@ -198,7 +201,7 @@ public class Client extends SimpleClient
         }
         else if (msgType.equals("REGISTER"))
         {
-            String type = line.substring(9).toUpperCase();
+            String type = toUpperCaseLocalized(line.substring(9));
             try
             {
                 return new RegisterMessage(Collections.singletonList(Enum.valueOf(Event.Type.class, type)));

src/java/org/apache/cassandra/transport/messages/StartupMessage.java

@@ -29,6 +29,9 @@ import org.apache.cassandra.service.QueryState;
 import org.apache.cassandra.transport.*;
 import org.apache.cassandra.utils.CassandraVersion;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 /**
  * The initial message of the protocol.
  * Sets up a number of connection options.
@@ -89,7 +92,7 @@ public class StartupMessage extends Message.Request
 
         if (options.containsKey(COMPRESSION))
         {
-            String compression = options.get(COMPRESSION).toLowerCase();
+            String compression = toLowerCaseLocalized(options.get(COMPRESSION));
             if (compression.equals("snappy"))
             {
                 if (Compressor.SnappyCompressor.instance == null)
@@ -158,7 +161,7 @@ public class StartupMessage extends Message.Request
     {
         Map<String, String> newMap = new HashMap<String, String>(options.size());
         for (Map.Entry<String, String> entry : options.entrySet())
-            newMap.put(entry.getKey().toUpperCase(), entry.getValue());
+            newMap.put(toUpperCaseLocalized(entry.getKey()), entry.getValue());
         return newMap;
     }
 

src/java/org/apache/cassandra/utils/FBUtilities.java

@@ -103,6 +103,7 @@ import static org.apache.cassandra.config.CassandraRelevantProperties.TRIGGERS_D
 import static org.apache.cassandra.config.CassandraRelevantProperties.USER_HOME;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
 import static org.apache.cassandra.utils.Clock.Global.nanoTime;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public class FBUtilities
 {
@@ -118,7 +119,7 @@ public class FBUtilities
     public static final BigInteger TWO = new BigInteger("2");
     private static final String DEFAULT_TRIGGER_DIR = "triggers";
 
-    private static final String OPERATING_SYSTEM = OS_NAME.getString().toLowerCase();
+    private static final String OPERATING_SYSTEM = toLowerCaseLocalized(OS_NAME.getString());
     public static final boolean isLinux = OPERATING_SYSTEM.contains("linux");
 
     private static volatile InetAddress localInetAddress;
@@ -1364,7 +1365,7 @@ public class FBUtilities
     public static String camelToSnake(String camel)
     {
         if (camel.chars().allMatch(Character::isUpperCase))
-            return camel.toLowerCase();
+            return toLowerCaseLocalized(camel);
 
         StringBuilder sb = new StringBuilder();
         for (char c : camel.toCharArray())
@@ -1374,7 +1375,7 @@ public class FBUtilities
                 // if first char is uppercase, then avoid adding the _ prefix
                 if (sb.length() > 0)
                     sb.append('_');
-                sb.append(Character.toLowerCase(c));
+                sb.append(Character.toLowerCase(c)); // checkstyle: permit this invocation
             }
             else
             {

src/java/org/apache/cassandra/utils/GuidGenerator.java

@@ -23,6 +23,7 @@ import java.util.Random;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.JAVA_SECURITY_EGD;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 public class GuidGenerator
 {
@@ -101,7 +102,7 @@ public class GuidGenerator
 
     private static String convertToStandardFormat(String valueAfterMD5)
     {
-        String raw = valueAfterMD5.toUpperCase();
+        String raw = toUpperCaseLocalized(valueAfterMD5);
         StringBuilder sb = new StringBuilder();
         sb.append(raw.substring(0, 8))
           .append("-")

src/java/org/apache/cassandra/utils/JsonUtils.java

@@ -23,7 +23,6 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Locale;
 import java.util.Map;
 
 import com.fasterxml.jackson.core.JsonFactory;
@@ -38,6 +37,7 @@ import org.apache.cassandra.io.util.FileOutputStreamPlus;
 import org.apache.cassandra.serializers.MarshalException;
 
 import static org.apache.cassandra.io.util.File.WriteMode.OVERWRITE;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public final class JsonUtils
 {
@@ -203,7 +203,7 @@ public final class JsonUtils
             }
 
             // otherwise, lowercase it if needed
-            String lowered = mapKey.toLowerCase(Locale.US);
+            String lowered = toLowerCaseLocalized(mapKey);
             if (!mapKey.equals(lowered))
                 valueMap.put(lowered, valueMap.remove(mapKey));
         }

src/java/org/apache/cassandra/utils/LocalizeString.java

@@ -0,0 +1,60 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.cassandra.utils;
+
+import java.util.Locale;
+
+public class LocalizeString
+{
+    /**
+     * Convert the String to lower case, using {@link java.util.Locale#US} by default
+     */
+    public static String toLowerCaseLocalized(String input)
+    {
+        return toLowerCaseLocalized(input, Locale.US);
+    }
+
+    /**
+     * @param input  The string to be converted to lower case.
+     * @param locale The locale to use for the conversion.
+     * @return String itself with lowercase and localized by your selection of {@link java.util.Locale}.
+     */
+    public static String toLowerCaseLocalized(String input, Locale locale)
+    {
+        return input.toLowerCase(locale); // checkstyle: permit this invocation
+    }
+
+    /**
+     * Convert the String to upper case, using {@link java.util.Locale#US} by default
+     */
+    public static String toUpperCaseLocalized(String input)
+    {
+        return toUpperCaseLocalized(input, Locale.US);
+    }
+
+    /**
+     * @param input  The string to be converted to uppercase.
+     * @param locale The locale to use for the conversion. This parameter is optional.
+     * @return String itself with uppercase and localized by your selection of {@link java.util.Locale}.
+     */
+    public static String toUpperCaseLocalized(String input, Locale locale)
+    {
+        return input.toUpperCase(locale); // checkstyle: permit this invocation
+    }
+}

src/java/org/apache/cassandra/utils/NativeLibrary.java

@@ -35,6 +35,7 @@ import org.apache.cassandra.io.FSWriteError;
 import static org.apache.cassandra.config.CassandraRelevantProperties.IGNORE_MISSING_NATIVE_FILE_HINTS;
 import static org.apache.cassandra.config.CassandraRelevantProperties.OS_ARCH;
 import static org.apache.cassandra.config.CassandraRelevantProperties.OS_NAME;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.apache.cassandra.utils.NativeLibrary.OSType.LINUX;
 import static org.apache.cassandra.utils.NativeLibrary.OSType.MAC;
 import static org.apache.cassandra.utils.NativeLibrary.OSType.AIX;
@@ -102,7 +103,7 @@ public final class NativeLibrary
             default: wrappedLibrary = new NativeLibraryLinux();
         }
 
-        if (OS_ARCH.getString().toLowerCase().contains("ppc"))
+        if (toLowerCaseLocalized(OS_ARCH.getString()).contains("ppc"))
         {
             if (osType == LINUX)
             {
@@ -134,7 +135,7 @@ public final class NativeLibrary
      */
     private static OSType getOsType()
     {
-        String osName = OS_NAME.getString().toLowerCase();
+        String osName = toLowerCaseLocalized(OS_NAME.getString());
         if  (osName.contains("linux"))
             return LINUX;
         else if (osName.contains("mac"))

src/java/org/apache/cassandra/utils/NativeSSTableLoaderClient.java

@@ -35,6 +35,8 @@ import org.apache.cassandra.dht.Token.TokenFactory;
 import org.apache.cassandra.io.sstable.SSTableLoader;
 import org.apache.cassandra.schema.TableMetadata;
 
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
+
 public class NativeSSTableLoaderClient extends SSTableLoader.Client
 {
     protected final Map<String, TableMetadataRef> tables;
@@ -203,7 +205,7 @@ public class NativeSSTableLoaderClient extends SSTableLoader.Client
 
     private static ColumnMetadata createDefinitionFromRow(Row row, String keyspace, String table, Types types)
     {
-        ClusteringOrder order = ClusteringOrder.valueOf(row.getString("clustering_order").toUpperCase());
+        ClusteringOrder order = ClusteringOrder.valueOf(toUpperCaseLocalized(row.getString("clustering_order")));
         AbstractType<?> type = CQLTypeParser.parse(keyspace, row.getString("type"), types);
         if (order == ClusteringOrder.DESC)
             type = ReversedType.getInstance(type);
@@ -211,7 +213,7 @@ public class NativeSSTableLoaderClient extends SSTableLoader.Client
         ColumnIdentifier name = new ColumnIdentifier(row.getBytes("column_name_bytes"), row.getString("column_name"));
 
         int position = row.getInt("position");
-        org.apache.cassandra.schema.ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(row.getString("kind").toUpperCase());
+        org.apache.cassandra.schema.ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(toUpperCaseLocalized(row.getString("kind")));
         return new ColumnMetadata(keyspace, table, name, type, position, kind, null);
     }
 
@@ -219,7 +221,7 @@ public class NativeSSTableLoaderClient extends SSTableLoader.Client
     {
         String name = row.getString("column_name");
         AbstractType<?> type = CQLTypeParser.parse(keyspace, row.getString("type"), Types.none());
-        ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(row.getString("kind").toUpperCase());
+        ColumnMetadata.Kind kind = ColumnMetadata.Kind.valueOf(toUpperCaseLocalized(row.getString("kind")));
         ColumnMetadata column = new ColumnMetadata(keyspace, table, ColumnIdentifier.getInterned(name, true), type, ColumnMetadata.NO_POSITION, kind, null);
         long droppedTime = row.getTimestamp("dropped_time").getTime();
         return new DroppedColumn(column, droppedTime);

src/java/org/apache/cassandra/utils/binlog/BinLog.java

@@ -54,6 +54,7 @@ import org.apache.cassandra.utils.concurrent.WeightedQueue;
 
 import static java.lang.String.format;
 import static org.apache.cassandra.config.CassandraRelevantProperties.CHRONICLE_ANNOUNCER_DISABLE;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 /**
  * Bin log is a is quick and dirty binary log that is kind of a NIH version of binary logging with a traditional logging
@@ -389,7 +390,7 @@ public class BinLog implements Runnable
         public Builder rollCycle(String rollCycle)
         {
             Preconditions.checkNotNull(rollCycle, "rollCycle was null");
-            rollCycle = rollCycle.toUpperCase();
+            rollCycle = toUpperCaseLocalized(rollCycle);
             Preconditions.checkNotNull(RollCycles.valueOf(rollCycle), "unrecognized roll cycle");
             this.rollCycle = rollCycle;
             return this;

test/distributed/org/apache/cassandra/distributed/Cluster.java

@@ -29,6 +29,8 @@ import org.apache.cassandra.distributed.impl.Instance;
 import org.apache.cassandra.distributed.shared.Versions;
 import org.apache.cassandra.net.Message;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * A simple cluster supporting only the 'current' Cassandra version, offering easy access to the convenience methods
  * of IInvokableInstance on each node.
@@ -81,7 +83,7 @@ public class Cluster extends AbstractCluster<IInvokableInstance>
             {
                 get(1).acceptsOnInstance((IIsolatedExecutor.SerializableConsumer<IMessage>) (msgPassed) -> {
                     Message decoded = Instance.deserializeMessage(msgPassed);
-                    if (!decoded.verb().toString().toLowerCase().contains("gossip"))
+                    if (!toLowerCaseLocalized(decoded.verb().toString()).contains("gossip"))
                         System.out.println(String.format("MSG %d -> %d: %s | %s", from, to, decoded, decoded.payload));
                 }).accept(msg);
             }

test/distributed/org/apache/cassandra/distributed/test/FailingRepairTest.java

@@ -76,6 +76,8 @@ import org.apache.cassandra.service.ActiveRepairService.ParentRepairStatus;
 import org.apache.cassandra.service.StorageService;
 import org.awaitility.Awaitility;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 @RunWith(Parameterized.class)
 public class FailingRepairTest extends TestBaseImpl implements Serializable
 {
@@ -132,7 +134,7 @@ public class FailingRepairTest extends TestBaseImpl implements Serializable
 
     private static String getCfName(Verb type, RepairParallelism parallelism, boolean withTracing)
     {
-        return type.name().toLowerCase() + "_" + parallelism.name().toLowerCase() + "_" + withTracing;
+        return toLowerCaseLocalized(type.name()) + "_" + toLowerCaseLocalized(parallelism.name()) + "_" + withTracing;
     }
 
     @BeforeClass

test/distributed/org/apache/cassandra/distributed/test/ReadDigestConsistencyTest.java

@@ -33,6 +33,8 @@ import org.apache.cassandra.exceptions.SyntaxException;
 import org.apache.cassandra.utils.Throwables;
 import org.apache.cassandra.utils.TimeUUID;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class ReadDigestConsistencyTest extends TestBaseImpl
 {
     private final static Logger logger = LoggerFactory.getLogger(ReadDigestConsistencyTest.class);
@@ -101,7 +103,7 @@ public class ReadDigestConsistencyTest extends TestBaseImpl
                                              Arrays.toString(boundValues),
                                              coordinator.instance().broadcastAddress(),
                                              coordinator.instance().getReleaseVersionString()),
-                               activity.toLowerCase().contains("mismatch for key"));
+                                             toLowerCaseLocalized(activity).contains("mismatch for key"));
         }
     }
 

test/distributed/org/apache/cassandra/distributed/test/RepairCoordinatorBase.java

@@ -35,6 +35,7 @@ import org.apache.cassandra.distributed.test.DistributedRepairUtils.RepairParall
 import org.apache.cassandra.distributed.test.DistributedRepairUtils.RepairType;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.NODETOOL_JMX_NOTIFICATION_POLL_INTERVAL_SECONDS;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public class RepairCoordinatorBase extends TestBaseImpl
 {
@@ -98,7 +99,7 @@ public class RepairCoordinatorBase extends TestBaseImpl
 
     protected String postfix()
     {
-        return repairType.name().toLowerCase() + "_" + parallelism.name().toLowerCase() + "_" + withNotifications;
+        return toLowerCaseLocalized(repairType.name()) + "_" + toLowerCaseLocalized(parallelism.name()) + "_" + withNotifications;
     }
 
     protected NodeToolResult repair(int node, String... args) {

test/distributed/org/apache/cassandra/distributed/test/RepairCoordinatorFailingMessageTest.java

@@ -42,6 +42,7 @@ import org.apache.cassandra.net.Verb;
 
 import static java.lang.String.format;
 import static org.apache.cassandra.distributed.api.IMessageFilters.Matcher.of;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 @RunWith(Parameterized.class)
 @Ignore("Until CASSANDRA-15566 is in these tests all time out")
@@ -100,7 +101,7 @@ public class RepairCoordinatorFailingMessageTest extends TestBaseImpl implements
 
     private String postfix()
     {
-        return repairType.name().toLowerCase();
+        return toLowerCaseLocalized(repairType.name());
     }
 
     private NodeToolResult repair(int node, String... args) {

test/distributed/org/apache/cassandra/distributed/test/SSTableIdGenerationTest.java

@@ -67,6 +67,7 @@ import static org.apache.cassandra.db.SystemKeyspace.LEGACY_SSTABLE_ACTIVITY;
 import static org.apache.cassandra.db.SystemKeyspace.SSTABLE_ACTIVITY_V2;
 import static org.apache.cassandra.distributed.shared.FutureUtils.waitOn;
 import static org.apache.cassandra.distributed.test.ExecUtil.rethrow;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.assertj.core.api.Assertions.assertThat;
 
 public class SSTableIdGenerationTest extends TestBaseImpl
@@ -176,7 +177,7 @@ public class SSTableIdGenerationTest extends TestBaseImpl
             // create a table and two sstables with sequential id for each strategy, the sstables will contain overlapping partitions
             for (Class<? extends AbstractCompactionStrategy> compactionStrategyClass : compactionStrategyClasses)
             {
-                String tableName = "tbl_" + compactionStrategyClass.getSimpleName().toLowerCase();
+                String tableName = "tbl_" + toLowerCaseLocalized(compactionStrategyClass.getSimpleName());
                 cluster.schemaChange(createTableStmt(KEYSPACE, tableName, compactionStrategyClass));
 
                 createSSTables(cluster.get(1), KEYSPACE, tableName, 1, 2);
@@ -189,7 +190,7 @@ public class SSTableIdGenerationTest extends TestBaseImpl
             // create another two sstables with uuid for each previously created table
             for (Class<? extends AbstractCompactionStrategy> compactionStrategyClass : compactionStrategyClasses)
             {
-                String tableName = "tbl_" + compactionStrategyClass.getSimpleName().toLowerCase();
+                String tableName = "tbl_" + toLowerCaseLocalized(compactionStrategyClass.getSimpleName());
 
                 createSSTables(cluster.get(1), KEYSPACE, tableName, 3, 4);
 

test/memory/org/apache/cassandra/db/compaction/CompactionAllocationTest.java

@@ -78,6 +78,8 @@ import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.ObjectSizes;
 import org.apache.cassandra.utils.concurrent.Refs;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class CompactionAllocationTest
 {
     private static final Logger logger = LoggerFactory.getLogger(CompactionAllocationTest.class);
@@ -494,7 +496,7 @@ public class CompactionAllocationTest
 
     private static void testTinyPartitions(String name, int numSSTable, int sstablePartitions, boolean overlap) throws Throwable
     {
-        String ksname = "ks_" + name.toLowerCase();
+        String ksname = "ks_" + toLowerCaseLocalized(name);
 
         SchemaLoader.createKeyspace(ksname, KeyspaceParams.simple(1),
                                     CreateTableStatement.parse("CREATE TABLE tbl (k INT PRIMARY KEY, v INT)", ksname).build());
@@ -603,7 +605,7 @@ public class CompactionAllocationTest
 
     private static void testMediumPartitions(String name, int numSSTable, int sstablePartitions, boolean overlap, boolean overlapCK) throws Throwable
     {
-        String ksname = "ks_" + name.toLowerCase();
+        String ksname = "ks_" + toLowerCaseLocalized(name);
 
         SchemaLoader.createKeyspace(ksname, KeyspaceParams.simple(1),
                                     CreateTableStatement.parse("CREATE TABLE tbl (k text, c text, v1 text, v2 text, v3 text, v4 text, PRIMARY KEY (k, c))", ksname).build());
@@ -702,7 +704,7 @@ public class CompactionAllocationTest
 
     private static void testWidePartitions(String name, int numSSTable, int sstablePartitions, boolean overlap, boolean overlapCK) throws Throwable
     {
-        String ksname = "ks_" + name.toLowerCase();
+        String ksname = "ks_" + toLowerCaseLocalized(name);
 
         SchemaLoader.createKeyspace(ksname, KeyspaceParams.simple(1),
                                     CreateTableStatement.parse("CREATE TABLE tbl (k text, c text, v1 text, v2 text, v3 text, v4 text, PRIMARY KEY (k, c))", ksname).build());
@@ -806,7 +808,7 @@ public class CompactionAllocationTest
                                                    int sstablePartitions,
                                                    IndexDef...indexes) throws Throwable
     {
-        String ksname = "ks_" + name.toLowerCase();
+        String ksname = "ks_" + toLowerCaseLocalized(name);
         SchemaLoader.createKeyspace(ksname, KeyspaceParams.simple(1),
                 CreateTableStatement.parse("CREATE TABLE tbl (k text, c text, v1 text, v2 text, v3 text, v4 text, PRIMARY KEY (k, c))", ksname).build());
 

test/simulator/main/org/apache/cassandra/simulator/Action.java

@@ -897,7 +897,7 @@ public abstract class Action implements PriorityQueueNode
                 continue;
 
             if (!transitive.is(modifier)) builder.append(modifier.displayId);
-            else builder.append(Character.toUpperCase(modifier.displayId));
+            else builder.append(Character.toUpperCase(modifier.displayId)); // checkstyle: permit this invocation
         }
 
         boolean hasTransitiveOnly = false;

test/simulator/main/org/apache/cassandra/simulator/SimulationRunner.java

@@ -81,6 +81,7 @@ import static org.apache.cassandra.simulator.debug.Record.record;
 import static org.apache.cassandra.simulator.debug.SelfReconcile.reconcileWithSelf;
 import static org.apache.cassandra.simulator.utils.IntRange.parseRange;
 import static org.apache.cassandra.simulator.utils.LongRange.parseNanosRange;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 
 @SuppressWarnings({ "ZeroLengthArrayAllocation", "CodeBlock2Expr", "SameParameterValue", "DynamicRegexReplaceableByCompiledPattern", "CallToSystemGC" })
 public class SimulationRunner
@@ -281,7 +282,7 @@ public class SimulationRunner
             Optional.ofNullable(topologyChanges).ifPresent(topologyChanges -> {
                 builder.topologyChanges(stream(topologyChanges.split(","))
                                         .filter(v -> !v.isEmpty())
-                                        .map(v -> TopologyChange.valueOf(v.toUpperCase()))
+                                        .map(v -> TopologyChange.valueOf(toUpperCaseLocalized(v)))
                                         .toArray(TopologyChange[]::new));
             });
             parseNanosRange(Optional.ofNullable(topologyChangeInterval)).ifPresent(builder::topologyChangeIntervalNanos);
@@ -289,7 +290,7 @@ public class SimulationRunner
             Optional.ofNullable(priority).ifPresent(kinds -> {
                 builder.scheduler(stream(kinds.split(","))
                                   .filter(v -> !v.isEmpty())
-                                  .map(v -> RunnableActionScheduler.Kind.valueOf(v.toUpperCase()))
+                                  .map(v -> RunnableActionScheduler.Kind.valueOf(toUpperCaseLocalized(v)))
                                   .toArray(RunnableActionScheduler.Kind[]::new));
             });
 

test/unit/org/apache/cassandra/SchemaLoader.java

@@ -52,6 +52,7 @@ import static org.apache.cassandra.config.CassandraRelevantProperties.ALLOW_UNSA
 import static org.apache.cassandra.config.CassandraRelevantProperties.TEST_COMPRESSION;
 import static org.apache.cassandra.config.CassandraRelevantProperties.TEST_COMPRESSION_ALGO;
 import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 
 public class SchemaLoader
 {
@@ -745,7 +746,7 @@ public static TableMetadata.Builder clusteringSASICFMD(String ksName, String cfN
 
     private static CompressionParams compressionParams(int chunkLength)
     {
-        String algo = TEST_COMPRESSION_ALGO.getString().toLowerCase();
+        String algo = toLowerCaseLocalized(TEST_COMPRESSION_ALGO.getString());
         switch (algo)
         {
             case "deflate":

test/unit/org/apache/cassandra/auth/CassandraNetworkAuthorizerTest.java

@@ -41,6 +41,7 @@ import static org.apache.cassandra.auth.AuthKeyspace.NETWORK_PERMISSIONS;
 import static org.apache.cassandra.auth.AuthTestUtils.auth;
 import static org.apache.cassandra.auth.AuthTestUtils.getRolesReadCount;
 import static org.apache.cassandra.schema.SchemaConstants.AUTH_KEYSPACE_NAME;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
@@ -100,7 +101,7 @@ public class CassandraNetworkAuthorizerTest extends CQLTester
 
     private static String createName()
     {
-        return RandomStringUtils.randomAlphabetic(8).toLowerCase();
+        return toLowerCaseLocalized(RandomStringUtils.randomAlphabetic(8));
     }
 
     private static DCPermissions dcPerms(String username)

test/unit/org/apache/cassandra/config/DataStorageSpecTest.java

@@ -28,6 +28,7 @@ import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.BYTES;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.GIBIBYTES;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.KIBIBYTES;
 import static org.apache.cassandra.config.DataStorageSpec.DataStorageUnit.MEBIBYTES;
+import static org.apache.cassandra.utils.LocalizeString.toUpperCaseLocalized;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.Assert.*;
 import static org.quicktheories.QuickTheory.qt;
@@ -242,7 +243,7 @@ public class DataStorageSpecTest
     {
         qt().forAll(gen()).check(there -> {
             DataStorageSpec.LongBytesBound back = new DataStorageSpec.LongBytesBound(there.toString());
-            DataStorageSpec.LongBytesBound BACK = new DataStorageSpec.LongBytesBound(there.toString().toUpperCase(Locale.ROOT).replace("I", "i"));
+            DataStorageSpec.LongBytesBound BACK = new DataStorageSpec.LongBytesBound(toUpperCaseLocalized(there.toString(), Locale.ROOT).replace("I", "i"));
             return there.equals(back) && there.equals(BACK);
         });
     }

test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java

@@ -282,6 +282,7 @@ public class DatabaseDescriptorRefTest
     "org.apache.cassandra.utils.CloseableIterator",
     "org.apache.cassandra.utils.FBUtilities",
     "org.apache.cassandra.utils.FBUtilities$1",
+    "org.apache.cassandra.utils.LocalizeString",
     "org.apache.cassandra.utils.SystemInfo",
     "org.apache.cassandra.utils.Pair",
     "org.apache.cassandra.utils.binlog.BinLogOptions",

test/unit/org/apache/cassandra/cql3/CQLTester.java

@@ -39,7 +39,6 @@ import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
-import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -204,6 +203,7 @@ import static org.apache.cassandra.cql3.SchemaElement.SchemaElementType.TABLE;
 import static org.apache.cassandra.cql3.SchemaElement.SchemaElementType.TYPE;
 import static org.apache.cassandra.metrics.CassandraMetricsRegistry.createMetricsKeyspaceTables;
 import static org.apache.cassandra.schema.SchemaConstants.VIRTUAL_METRICS;
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
@@ -1046,7 +1046,7 @@ public abstract class CQLTester
     private String createSchemaElementName(SchemaElement.SchemaElementType type, String keyspace)
     {
         String prefix = keyspace == null ? "" : keyspace + '.';
-        String typeName = type == MATERIALIZED_VIEW ? "mv" : type.name().toLowerCase(Locale.US);
+        String typeName = type == MATERIALIZED_VIEW ? "mv" : toLowerCaseLocalized(type.name());
         int sequence = seqNumber.getAndIncrement();
         int usedSpaceSoFar = prefix.length() + typeName.length() + Math.max(2, numberOfDigits(sequence)) + 1;
         String testMethodName = StringUtils.truncate(getTestMethodName(), SchemaConstants.NAME_LENGTH - usedSpaceSoFar);
@@ -1329,7 +1329,7 @@ public abstract class CQLTester
 
         index = ParseUtils.isQuoted(index, '\"')
                 ? ParseUtils.unDoubleQuote(index)
-                : index.toLowerCase();
+                : toLowerCaseLocalized(index);
 
         return Pair.create(keyspace, index);
     }
@@ -2738,7 +2738,7 @@ public abstract class CQLTester
 
     private String getTestMethodName()
     {
-        return decorateCQLWithTestNames && testName.getMethodName() != null ? '_' + testName.getMethodName().toLowerCase().replaceAll("[^\\w]", "_")
+        return decorateCQLWithTestNames && testName.getMethodName() != null ? '_' + toLowerCaseLocalized(testName.getMethodName()).replaceAll("[^\\w]", "_")
                                                                             : "";
     }
 

test/unit/org/apache/cassandra/cql3/KeywordTestBase.java

@@ -31,6 +31,8 @@ import org.junit.Test;
 
 import org.apache.cassandra.exceptions.SyntaxException;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 /**
  * This class tests all keywords which took a long time. Hence it was split into multiple
  * KeywordTestSplitN to prevent CI timing out. If timeouts reappear split it further
@@ -105,7 +107,7 @@ public abstract class KeywordTestBase extends CQLTester
             logger.info(selectStatement);
             rs = execute(selectStatement);
             row = rs.one();
-            String value = row.getString(keyword.toLowerCase());
+            String value = row.getString(toLowerCaseLocalized(keyword));
             Assert.assertEquals(keyword, value);
 
             /* Make a materialized view using the fields (cannot re-use the name as MV must be in same keyspace).

test/unit/org/apache/cassandra/cql3/functions/NativeFunctionsTest.java

@@ -29,6 +29,8 @@ import org.apache.cassandra.schema.SchemaConstants;
 import org.apache.cassandra.schema.UserFunctions;
 import org.assertj.core.api.Assertions;
 
+import static org.apache.cassandra.utils.LocalizeString.toLowerCaseLocalized;
+
 public class NativeFunctionsTest
 {
     /**
@@ -154,7 +156,7 @@ public class NativeFunctionsTest
             Assertions.assertThat(function.argTypes()).isEqualTo(newFunction.argTypes());
             Assertions.assertThat(function.returnType()).isEqualTo(newFunction.returnType());
             Assertions.assertThat(function.getClass()).isEqualTo(newFunction.getClass());
-            Assertions.assertThat(function.name().name.toLowerCase())
+            Assertions.assertThat(toLowerCaseLocalized(function.name().name))
                       .isEqualTo(StringUtils.remove(newFunction.name().name, '_'));
         }
     }
@@ -190,7 +192,7 @@ public class NativeFunctionsTest
             Assertions.assertThat(factory.name).isNotEqualTo(newFactory.name);
             Assertions.assertThat(factory.parameters).isEqualTo(newFactory.parameters);
             Assertions.assertThat(factory.getClass()).isEqualTo(newFactory.getClass());
-            Assertions.assertThat(factory.name().name.toLowerCase())
+            Assertions.assertThat(toLowerCaseLocalized(factory.name().name))
                       .isEqualTo(StringUtils.remove(newFactory.name().name, '_'));
         }
     }
@@ -198,7 +200,7 @@ public class NativeFunctionsTest
     private static boolean satisfiesConventions(FunctionName functionName)
     {
         String name = functionName.name;
-        return name.equals(name.toLowerCase()) &&
+        return name.equals(toLowerCaseLocalized(name)) &&
                !LEGACY_FUNCTION_NAMES.containsKey(name);
     }
 }