Effective Locales

paper-api/src/main/java/org/bukkit/entity/Player.java

@@ -3275,6 +3275,22 @@ default boolean hasResourcePack() {
      */
     java.util.Locale locale();
     // Paper end
+
+    /**
+     * Returns the locale the server will use to send messages translated via the Adventure global translator.
+     * By default, the value of {@link Player#locale()} is used.
+     *
+     * @return the locale.
+     */
+    java.util.Locale getEffectiveLocale();
+
+    /**
+     * Change the locale the server will be translating its messages to.
+     *
+     * @param locale the locale to translate to
+     */
+    void setEffectiveLocale(java.util.@Nullable Locale locale);
+
     /**
      * Gets the player's estimated ping in milliseconds.
      *

paper-server/patches/sources/net/minecraft/server/level/ServerPlayer.java.patch

@@ -1,12 +1,13 @@
 --- a/net/minecraft/server/level/ServerPlayer.java
 +++ b/net/minecraft/server/level/ServerPlayer.java
-@@ -235,7 +_,8 @@
+@@ -235,7 +_,9 @@
      private int levitationStartTime;
      private boolean disconnected;
      private int requestedViewDistance = 2;
 -    public String language = "en_us";
 +    public String language = null; // Paper - default to null
 +    public java.util.Locale adventure$locale = java.util.Locale.US; // Paper
++    public java.util.Locale effectiveLocale = null; // Paper
      @Nullable
      private Vec3 startingToFallPosition;
      @Nullable

paper-server/patches/sources/net/minecraft/server/network/ServerConfigurationPacketListenerImpl.java.patch

@@ -42,7 +42,7 @@
      @Override
      public void handleClientInformation(ServerboundClientInformationPacket packet) {
          this.clientInformation = packet.information();
-+        this.connection.channel.attr(io.papermc.paper.adventure.PaperAdventure.LOCALE_ATTRIBUTE).set(net.kyori.adventure.translation.Translator.parseLocale(packet.information().language())); // Paper
++        this.connection.channel.attr(io.papermc.paper.adventure.PaperAdventure.LOCALE_ATTRIBUTE).set(player.effectiveLocale != null ? player.effectiveLocale : net.kyori.adventure.translation.Translator.parseLocale(packet.information().language())); // Paper
      }
 
      @Override

paper-server/patches/sources/net/minecraft/server/network/ServerGamePacketListenerImpl.java.patch

@@ -2513,7 +2513,7 @@
 +        // Paper end - do not accept invalid information
          boolean isModelPartShown = this.player.isModelPartShown(PlayerModelPart.HAT);
          this.player.updateOptions(packet.information());
-+        this.connection.channel.attr(io.papermc.paper.adventure.PaperAdventure.LOCALE_ATTRIBUTE).set(net.kyori.adventure.translation.Translator.parseLocale(packet.information().language())); // Paper
++        this.connection.channel.attr(io.papermc.paper.adventure.PaperAdventure.LOCALE_ATTRIBUTE).set(player.effectiveLocale != null ? player.effectiveLocale : net.kyori.adventure.translation.Translator.parseLocale(packet.information().language())); // Paper
          if (this.player.isModelPartShown(PlayerModelPart.HAT) != isModelPartShown) {
              this.server.getPlayerList().broadcastAll(new ClientboundPlayerInfoUpdatePacket(ClientboundPlayerInfoUpdatePacket.Action.UPDATE_HAT, this.player));
          }

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -2996,6 +2996,25 @@ public java.util.Locale locale() {
         return getHandle().adventure$locale;
     }
     // Paper end
+
+
+    @Override
+    public java.util.Locale getEffectiveLocale() {
+        if (getHandle().effectiveLocale == null) {
+            return locale();
+        }
+        return getHandle().effectiveLocale;
+    }
+
+    @Override
+    public void setEffectiveLocale(final java.util.Locale locale) {
+        getHandle().effectiveLocale = locale;
+
+        if (getHandle().connection != null) {
+            getHandle().connection.connection.channel.attr(io.papermc.paper.adventure.PaperAdventure.LOCALE_ATTRIBUTE).set(getEffectiveLocale());
+        }
+    }
+
     @Override
     public int getPing() {
         return this.getHandle().connection.latency();