diff --git a/paper-server/checkstyle.xml b/paper-server/checkstyle.xml
index ec61ec7570..5c7f6a5d51 100644
--- a/paper-server/checkstyle.xml
+++ b/paper-server/checkstyle.xml
@@ -26,6 +26,16 @@
         <property name="files" value=".*[/\\]net[/\\]minecraft[/\\].*"/>
     </module>
 
+    <!-- See SPIGOT-7676: Enforce Locale, to prevent issues with turkish 'I' and similar -->
+    <module name="RegexpSingleline">
+        <property name="format" value="\.toUpperCase\(\s*\)" />
+        <property name="message" value="Use toUpperCase(Locale.ROOT) instead of toUpperCase()" />
+    </module>
+    <module name="RegexpSingleline">
+        <property name="format" value="\.toLowerCase\(\s*\)" />
+        <property name="message" value="Use toLowerCase(Locale.ROOT) instead of toLowerCase()" />
+    </module>
+
     <module name="TreeWalker">
         <!-- See https://checkstyle.org/config_javadoc.html -->
         <module name="AtclauseOrder"/>
diff --git a/paper-server/nms-patches/net/minecraft/server/MinecraftServer.patch b/paper-server/nms-patches/net/minecraft/server/MinecraftServer.patch
index 77acf286fc..7d289eb047 100644
--- a/paper-server/nms-patches/net/minecraft/server/MinecraftServer.patch
+++ b/paper-server/nms-patches/net/minecraft/server/MinecraftServer.patch
@@ -188,7 +188,7 @@
 +                dimension = -999;
 +            }
 +
-+            String worldType = (dimension == -999) ? dimensionKey.location().getNamespace() + "_" + dimensionKey.location().getPath() : org.bukkit.World.Environment.getEnvironment(dimension).toString().toLowerCase();
++            String worldType = (dimension == -999) ? dimensionKey.location().getNamespace() + "_" + dimensionKey.location().getPath() : org.bukkit.World.Environment.getEnvironment(dimension).toString().toLowerCase(Locale.ROOT);
 +            String name = (dimensionKey == WorldDimension.OVERWORLD) ? s : s + "_" + worldType;
 +            if (dimension != 0) {
 +                File newWorld = Convertable.getStorageFolder(new File(name).toPath(), dimensionKey).toFile();
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 6b341eece4..18e347dd5e 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -584,10 +584,10 @@ public final class CraftServer implements Server {
             return found;
         }
 
-        String lowerName = name.toLowerCase(java.util.Locale.ENGLISH);
+        String lowerName = name.toLowerCase(Locale.ROOT);
         int delta = Integer.MAX_VALUE;
         for (Player player : getOnlinePlayers()) {
-            if (player.getName().toLowerCase(java.util.Locale.ENGLISH).startsWith(lowerName)) {
+            if (player.getName().toLowerCase(Locale.ROOT).startsWith(lowerName)) {
                 int curDelta = Math.abs(player.getName().length() - lowerName.length());
                 if (curDelta < delta) {
                     found = player;
@@ -641,7 +641,7 @@ public final class CraftServer implements Server {
                 matchedPlayers.add(iterPlayer);
                 break;
             }
-            if (iterPlayerName.toLowerCase(java.util.Locale.ENGLISH).contains(partialName.toLowerCase(java.util.Locale.ENGLISH))) {
+            if (iterPlayerName.toLowerCase(Locale.ROOT).contains(partialName.toLowerCase(Locale.ROOT))) {
                 // Partial match
                 matchedPlayers.add(iterPlayer);
             }
@@ -1203,7 +1203,7 @@ public final class CraftServer implements Server {
         } else if (name.equals(levelName + "_the_end")) {
             worldKey = net.minecraft.world.level.World.END;
         } else {
-            worldKey = ResourceKey.create(Registries.DIMENSION, new MinecraftKey(name.toLowerCase(java.util.Locale.ENGLISH)));
+            worldKey = ResourceKey.create(Registries.DIMENSION, new MinecraftKey(name.toLowerCase(Locale.ROOT)));
         }
 
         // If set to not keep spawn in memory (changed from default) then adjust rule accordingly
@@ -1213,7 +1213,7 @@ public final class CraftServer implements Server {
         WorldServer internal = (WorldServer) new WorldServer(console, console.executor, worldSession, worlddata, worldKey, worlddimension, getServer().progressListenerFactory.create(worlddata.getGameRules().getInt(GameRules.RULE_SPAWN_CHUNK_RADIUS)),
                 worlddata.isDebugWorld(), j, creator.environment() == Environment.NORMAL ? list : ImmutableList.of(), true, console.overworld().getRandomSequences(), creator.environment(), generator, biomeProvider);
 
-        if (!(worlds.containsKey(name.toLowerCase(java.util.Locale.ENGLISH)))) {
+        if (!(worlds.containsKey(name.toLowerCase(Locale.ROOT)))) {
             return null;
         }
 
@@ -1273,7 +1273,7 @@ public final class CraftServer implements Server {
             getLogger().log(Level.SEVERE, null, ex);
         }
 
-        worlds.remove(world.getName().toLowerCase(java.util.Locale.ENGLISH));
+        worlds.remove(world.getName().toLowerCase(Locale.ROOT));
         console.removeLevel(handle);
         return true;
     }
@@ -1286,7 +1286,7 @@ public final class CraftServer implements Server {
     public World getWorld(String name) {
         Preconditions.checkArgument(name != null, "name cannot be null");
 
-        return worlds.get(name.toLowerCase(java.util.Locale.ENGLISH));
+        return worlds.get(name.toLowerCase(Locale.ROOT));
     }
 
     @Override
@@ -1305,7 +1305,7 @@ public final class CraftServer implements Server {
             System.out.println("World " + world.getName() + " is a duplicate of another world and has been prevented from loading. Please delete the uid.dat file from " + world.getName() + "'s world directory if you want to be able to load the duplicate world.");
             return;
         }
-        worlds.put(world.getName().toLowerCase(java.util.Locale.ENGLISH), world);
+        worlds.put(world.getName().toLowerCase(Locale.ROOT), world);
     }
 
     @Override
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java b/paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
index 169e383086..fff6875dcf 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
@@ -5,6 +5,7 @@ import com.google.common.collect.ImmutableMap.Builder;
 import com.google.gson.JsonParseException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.regex.Matcher;
@@ -80,7 +81,7 @@ public final class CraftChatMessage {
                 }
                 switch (groupId) {
                 case 1:
-                    char c = match.toLowerCase(java.util.Locale.ENGLISH).charAt(1);
+                    char c = match.toLowerCase(Locale.ROOT).charAt(1);
                     EnumChatFormat format = formatMap.get(c);
 
                     if (c == 'x') {
diff --git a/paper-server/src/test/java/org/bukkit/SoundTest.java b/paper-server/src/test/java/org/bukkit/SoundTest.java
index ff62148d66..5137b2213a 100644
--- a/paper-server/src/test/java/org/bukkit/SoundTest.java
+++ b/paper-server/src/test/java/org/bukkit/SoundTest.java
@@ -3,6 +3,7 @@ package org.bukkit;
 import static org.bukkit.support.MatcherAssert.*;
 import static org.hamcrest.Matchers.*;
 import static org.junit.jupiter.api.Assertions.*;
+import java.util.Locale;
 import net.minecraft.core.registries.BuiltInRegistries;
 import net.minecraft.resources.MinecraftKey;
 import org.bukkit.craftbukkit.CraftSound;
@@ -21,7 +22,7 @@ public class SoundTest extends AbstractTestingBase {
     @Test
     public void testReverse() {
         for (MinecraftKey effect : BuiltInRegistries.SOUND_EVENT.keySet()) {
-            assertNotNull(Sound.valueOf(effect.getPath().replace('.', '_').toUpperCase(java.util.Locale.ENGLISH)), effect + "");
+            assertNotNull(Sound.valueOf(effect.getPath().replace('.', '_').toUpperCase(Locale.ROOT)), effect + "");
         }
     }
 
diff --git a/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/DeprecatedItemMetaCustomValueTest.java b/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/DeprecatedItemMetaCustomValueTest.java
index d4ffcee4a6..89403f0401 100644
--- a/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/DeprecatedItemMetaCustomValueTest.java
+++ b/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/DeprecatedItemMetaCustomValueTest.java
@@ -4,6 +4,7 @@ import static org.junit.jupiter.api.Assertions.*;
 import java.io.StringReader;
 import java.lang.reflect.Array;
 import java.nio.ByteBuffer;
+import java.util.Locale;
 import java.util.Map;
 import java.util.UUID;
 import org.bukkit.Bukkit;
@@ -82,7 +83,7 @@ public class DeprecatedItemMetaCustomValueTest extends AbstractTestingBase {
     }
 
     private NamespacedKey requestKey(String keyName) {
-        return new NamespacedKey("test-plugin", keyName.toLowerCase());
+        return new NamespacedKey("test-plugin", keyName.toLowerCase(Locale.ROOT));
     }
 
     /*
diff --git a/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PersistentDataContainerTest.java b/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PersistentDataContainerTest.java
index ac78dc6315..bb8e1e7e82 100644
--- a/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PersistentDataContainerTest.java
+++ b/paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PersistentDataContainerTest.java
@@ -7,6 +7,7 @@ import java.lang.reflect.Array;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.UUID;
 import java.util.function.BiConsumer;
@@ -96,7 +97,7 @@ public class PersistentDataContainerTest extends AbstractTestingBase {
     }
 
     private static NamespacedKey requestKey(String keyName) {
-        return new NamespacedKey("test-plugin", keyName.toLowerCase());
+        return new NamespacedKey("test-plugin", keyName.toLowerCase(Locale.ROOT));
     }
 
     @Test
diff --git a/paper-server/src/test/java/org/bukkit/generator/structure/StructureTest.java b/paper-server/src/test/java/org/bukkit/generator/structure/StructureTest.java
index 8c0669cf93..2c7e2236aa 100644
--- a/paper-server/src/test/java/org/bukkit/generator/structure/StructureTest.java
+++ b/paper-server/src/test/java/org/bukkit/generator/structure/StructureTest.java
@@ -3,6 +3,7 @@ package org.bukkit.generator.structure;
 import static org.junit.jupiter.api.Assertions.*;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
+import java.util.Locale;
 import net.minecraft.core.IRegistry;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.MinecraftKey;
@@ -25,7 +26,7 @@ public class StructureTest extends AbstractTestingBase {
             }
 
             String name = field.getName();
-            assertNotNull(Registry.STRUCTURE.get(NamespacedKey.fromString(name.toLowerCase())), "No structure for field name " + name);
+            assertNotNull(Registry.STRUCTURE.get(NamespacedKey.fromString(name.toLowerCase(Locale.ROOT))), "No structure for field name " + name);
         }
     }
 
@@ -36,7 +37,7 @@ public class StructureTest extends AbstractTestingBase {
             MinecraftKey minecraftKey = structureBuiltInRegistries.getKey(structure);
 
             try {
-                Structure bukkit = (Structure) Structure.class.getField(minecraftKey.getPath().toUpperCase()).get(null);
+                Structure bukkit = (Structure) Structure.class.getField(minecraftKey.getPath().toUpperCase(Locale.ROOT)).get(null);
 
                 assertEquals(minecraftKey, CraftNamespacedKey.toMinecraft(bukkit.getKey()), "Keys are not the same for " + minecraftKey);
             } catch (NoSuchFieldException e) {
diff --git a/paper-server/src/test/java/org/bukkit/generator/structure/StructureTypeTest.java b/paper-server/src/test/java/org/bukkit/generator/structure/StructureTypeTest.java
index 69bccab363..942ff7cd34 100644
--- a/paper-server/src/test/java/org/bukkit/generator/structure/StructureTypeTest.java
+++ b/paper-server/src/test/java/org/bukkit/generator/structure/StructureTypeTest.java
@@ -3,6 +3,7 @@ package org.bukkit.generator.structure;
 import static org.junit.jupiter.api.Assertions.*;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
+import java.util.Locale;
 import net.minecraft.core.registries.BuiltInRegistries;
 import net.minecraft.resources.MinecraftKey;
 import org.bukkit.NamespacedKey;
@@ -24,7 +25,7 @@ public class StructureTypeTest extends AbstractTestingBase {
             }
 
             String name = field.getName();
-            assertNotNull(Registry.STRUCTURE_TYPE.get(NamespacedKey.fromString(name.toLowerCase())), "No enchantment for field name " + name);
+            assertNotNull(Registry.STRUCTURE_TYPE.get(NamespacedKey.fromString(name.toLowerCase(Locale.ROOT))), "No enchantment for field name " + name);
         }
     }
 
@@ -34,7 +35,7 @@ public class StructureTypeTest extends AbstractTestingBase {
             MinecraftKey minecraftKey = BuiltInRegistries.STRUCTURE_TYPE.getKey(structureType);
 
             try {
-                StructureType bukkit = (StructureType) StructureType.class.getField(minecraftKey.getPath().toUpperCase()).get(null);
+                StructureType bukkit = (StructureType) StructureType.class.getField(minecraftKey.getPath().toUpperCase(Locale.ROOT)).get(null);
 
                 assertEquals(minecraftKey, CraftNamespacedKey.toMinecraft(bukkit.getKey()), "Keys are not the same for " + minecraftKey);
             } catch (NoSuchFieldException e) {
diff --git a/paper-server/src/test/java/org/bukkit/registry/RegistryConstantsTest.java b/paper-server/src/test/java/org/bukkit/registry/RegistryConstantsTest.java
index 38b73d90fe..f50c944d48 100644
--- a/paper-server/src/test/java/org/bukkit/registry/RegistryConstantsTest.java
+++ b/paper-server/src/test/java/org/bukkit/registry/RegistryConstantsTest.java
@@ -5,6 +5,7 @@ import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import net.minecraft.core.IRegistry;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.MinecraftKey;
@@ -48,7 +49,7 @@ public class RegistryConstantsTest extends AbstractTestingBase {
             }
 
             String name = field.getName();
-            NamespacedKey key = NamespacedKey.fromString(name.toLowerCase());
+            NamespacedKey key = NamespacedKey.fromString(name.toLowerCase(Locale.ROOT));
             if (registry.get(key) == null) {
                 excessKeys.add(key);
             }
@@ -67,7 +68,7 @@ public class RegistryConstantsTest extends AbstractTestingBase {
 
             try {
                 @SuppressWarnings("unchecked")
-                T bukkitObject = (T) clazz.getField(minecraftKey.getPath().toUpperCase()).get(null);
+                T bukkitObject = (T) clazz.getField(minecraftKey.getPath().toUpperCase(Locale.ROOT)).get(null);
 
                 assertEquals(minecraftKey, CraftNamespacedKey.toMinecraft(bukkitObject.getKey()), "Keys are not the same for " + minecraftKey);
             } catch (NoSuchFieldException e) {