add /language command (#780)

* Fix the following issues:
1. HashMap non-thread-safe issus
2. Fix the same problem in pr621, but use a better implementation

Add the following functions:
1. There is now a language cache inside getLanguage to prepare for different languages corresponding to different time zones where the accounts in the server are located

* add /language command,each account has their own Locate

src/main/java/emu/grasscutter/command/commands/PositionCommand.java

@@ -15,12 +15,12 @@ public final class PositionCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         Position pos = targetPlayer.getPos();
-        CommandHandler.sendMessage(sender, translate("commands.position.success",
+        CommandHandler.sendMessage(sender, translate(sender, "commands.position.success",
                 Float.toString(pos.getX()), Float.toString(pos.getY()), Float.toString(pos.getZ()),
                 Integer.toString(targetPlayer.getSceneId())));
     }

src/main/java/emu/grasscutter/command/commands/ReloadCommand.java

@@ -14,7 +14,7 @@ public final class ReloadCommand implements CommandHandler {
 
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
-        CommandHandler.sendMessage(sender, translate("commands.reload.reload_start"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.reload.reload_start"));
         
         Grasscutter.loadConfig();
         Grasscutter.loadLanguage();
@@ -23,6 +23,6 @@ public final class ReloadCommand implements CommandHandler {
         Grasscutter.getGameServer().getShopManager().load();
         Grasscutter.getDispatchServer().loadQueries();
         
-        CommandHandler.sendMessage(sender, translate("commands.reload.reload_done"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.reload.reload_done"));
     }
 }

src/main/java/emu/grasscutter/command/commands/ResetConstCommand.java

@@ -17,13 +17,13 @@ public final class ResetConstCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         if (args.size() > 0 && args.get(0).equalsIgnoreCase("all")) {
             targetPlayer.getAvatars().forEach(this::resetConstellation);
-            CommandHandler.sendMessage(sender, translate("commands.resetConst.reset_all"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.resetConst.reset_all"));
         } else {
             EntityAvatar entity = targetPlayer.getTeamManager().getCurrentAvatarEntity();
             if (entity == null) {
@@ -33,7 +33,7 @@ public final class ResetConstCommand implements CommandHandler {
             Avatar avatar = entity.getAvatar();
             this.resetConstellation(avatar);
 
-            CommandHandler.sendMessage(sender, translate("commands.resetConst.success", avatar.getAvatarData().getName()));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.resetConst.success", avatar.getAvatarData().getName()));
         }
     }
 

src/main/java/emu/grasscutter/command/commands/ResetShopLimitCommand.java

@@ -15,12 +15,12 @@ public final class ResetShopLimitCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         targetPlayer.getShopLimit().forEach(x -> x.setNextRefreshTime(0));
         targetPlayer.save();
-        CommandHandler.sendMessage(sender, translate("commands.status.success"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.status.success"));
     }
 }

src/main/java/emu/grasscutter/command/commands/SendMailCommand.java

@@ -39,7 +39,7 @@ public final class SendMailCommand implements CommandHandler {
                     MailBuilder mailBuilder;
                     switch (args.get(0).toLowerCase()) {
                         case "help" -> {
-                            CommandHandler.sendMessage(sender, translate(this.getClass().getAnnotation(Command.class).description()) + "\nUsage: " + this.getClass().getAnnotation(Command.class).usage());
+                            CommandHandler.sendMessage(sender, translate(sender, this.getClass().getAnnotation(Command.class).description()) + "\nUsage: " + this.getClass().getAnnotation(Command.class).usage());
                             return;
                         }
                         case "all" -> mailBuilder = new MailBuilder(true, new Mail());
@@ -47,16 +47,16 @@ public final class SendMailCommand implements CommandHandler {
                             if (DatabaseHelper.getPlayerById(Integer.parseInt(args.get(0))) != null) {
                                 mailBuilder = new MailBuilder(Integer.parseInt(args.get(0)), new Mail());
                             } else {
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.user_not_exist", args.get(0)));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.user_not_exist", args.get(0)));
                                 return;
                             }
                         }
                     }
                     mailBeingConstructed.put(senderId, mailBuilder);
-                    CommandHandler.sendMessage(sender, translate("commands.sendMail.start_composition"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.start_composition"));
                 }
-                case 2 -> CommandHandler.sendMessage(sender, translate("commands.sendMail.templates"));
-                default -> CommandHandler.sendMessage(sender, translate("commands.sendMail.invalid_arguments"));
+                case 2 -> CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.templates"));
+                default -> CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.invalid_arguments"));
             }
         } else {
             MailBuilder mailBuilder = mailBeingConstructed.get(senderId);
@@ -65,28 +65,28 @@ public final class SendMailCommand implements CommandHandler {
                 switch (args.get(0).toLowerCase()) {
                     case "stop" -> {
                         mailBeingConstructed.remove(senderId);
-                        CommandHandler.sendMessage(sender, translate("commands.sendMail.sendCancel"));
+                        CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.sendCancel"));
                         return;
                     }
                     case "finish" -> {
                         if (mailBuilder.constructionStage == 3) {
                             if (!mailBuilder.sendToAll) {
                                 Grasscutter.getGameServer().getPlayerByUid(mailBuilder.recipient, true).sendMail(mailBuilder.mail);
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.send_done", Integer.toString(mailBuilder.recipient)));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.send_done", Integer.toString(mailBuilder.recipient)));
                             } else {
                                 for (Player player : DatabaseHelper.getAllPlayers()) {
                                     Grasscutter.getGameServer().getPlayerByUid(player.getUid(), true).sendMail(mailBuilder.mail);
                                 }
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.send_all_done"));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.send_all_done"));
                             }
                             mailBeingConstructed.remove(senderId);
                         } else {
-                            CommandHandler.sendMessage(sender, translate("commands.sendMail.not_composition_end", getConstructionArgs(mailBuilder.constructionStage)));
+                            CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.not_composition_end", getConstructionArgs(mailBuilder.constructionStage, sender)));
                         }
                         return;
                     }
                     case "help" -> {
-                        CommandHandler.sendMessage(sender, translate("commands.sendMail.please_use", getConstructionArgs(mailBuilder.constructionStage)));
+                        CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.please_use", getConstructionArgs(mailBuilder.constructionStage, sender)));
                         return;
                     }
                     default -> {
@@ -94,19 +94,19 @@ public final class SendMailCommand implements CommandHandler {
                             case 0 -> {
                                 String title = String.join(" ", args.subList(0, args.size()));
                                 mailBuilder.mail.mailContent.title = title;
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.set_title", title));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.set_title", title));
                                 mailBuilder.constructionStage++;
                             }
                             case 1 -> {
                                 String contents = String.join(" ", args.subList(0, args.size()));
                                 mailBuilder.mail.mailContent.content = contents;
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.set_contents", contents));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.set_contents", contents));
                                 mailBuilder.constructionStage++;
                             }
                             case 2 -> {
                                 String msgSender = String.join(" ", args.subList(0, args.size()));
                                 mailBuilder.mail.mailContent.sender = msgSender;
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.set_message_sender", msgSender));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.set_message_sender", msgSender));
                                 mailBuilder.constructionStage++;
                             }
                             case 3 -> {
@@ -119,21 +119,21 @@ public final class SendMailCommand implements CommandHandler {
                                         try {
                                             refinement = Integer.parseInt(args.get(3));
                                         } catch (NumberFormatException ignored) {
-                                            CommandHandler.sendMessage(sender, translate("commands.generic.invalid.itemRefinement"));
+                                            CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.itemRefinement"));
                                             return;
                                         }  // Fallthrough
                                     case 3: // <itemId|itemName> [amount] [level]
                                         try {
                                             lvl = Integer.parseInt(args.get(2));
                                         } catch (NumberFormatException ignored) {
-                                            CommandHandler.sendMessage(sender, translate("commands.generic.invalid.itemLevel"));
+                                            CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.itemLevel"));
                                             return;
                                         }  // Fallthrough
                                     case 2: // <itemId|itemName> [amount]
                                         try {
                                             amount = Integer.parseInt(args.get(1));
                                         } catch (NumberFormatException ignored) {
-                                            CommandHandler.sendMessage(sender, translate("commands.generic.invalid.amount"));
+                                            CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.amount"));
                                             return;
                                         }  // Fallthrough
                                     case 1: // <itemId|itemName>
@@ -141,33 +141,33 @@ public final class SendMailCommand implements CommandHandler {
                                             item = Integer.parseInt(args.get(0));
                                         } catch (NumberFormatException ignored) {
                                             // TODO: Parse from item name using GM Handbook.
-                                            CommandHandler.sendMessage(sender, translate("commands.generic.invalid.itemId"));
+                                            CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.itemId"));
                                             return;
                                         }
                                         break;
                                     default: // *No args*
-                                        CommandHandler.sendMessage(sender, translate("commands.give.usage"));
+                                        CommandHandler.sendMessage(sender, translate(sender, "commands.give.usage"));
                                         return;
                                 }
                                 mailBuilder.mail.itemList.add(new Mail.MailItem(item, amount, lvl));
-                                CommandHandler.sendMessage(sender, translate("commands.sendMail.send", Integer.toString(amount), Integer.toString(item), Integer.toString(lvl)));
+                                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.send", Integer.toString(amount), Integer.toString(item), Integer.toString(lvl)));
                             }
                         }
                     }
                 }
             } else {
-                CommandHandler.sendMessage(sender, translate("commands.sendMail.invalid_arguments_please_use", getConstructionArgs(mailBuilder.constructionStage)));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.sendMail.invalid_arguments_please_use", getConstructionArgs(mailBuilder.constructionStage, sender)));
             }
         }
     }
 
-    private String getConstructionArgs(int stage) {
+    private String getConstructionArgs(int stage, Player sender) {
         return switch(stage) {
-            case 0 -> translate("commands.sendMail.title");
-            case 1 -> translate("commands.sendMail.message");
-            case 2 -> translate("commands.sendMail.sender");
-            case 3 -> translate("commands.sendMail.arguments");
-            default -> translate("commands.sendMail.error", Integer.toString(stage));
+            case 0 -> translate(sender, "commands.sendMail.title");
+            case 1 -> translate(sender, "commands.sendMail.message");
+            case 2 -> translate(sender, "commands.sendMail.sender");
+            case 3 -> translate(sender, "commands.sendMail.arguments");
+            default -> translate(sender, "commands.sendMail.error", Integer.toString(stage));
         };
     }
 

src/main/java/emu/grasscutter/command/commands/SendMessageCommand.java

@@ -15,16 +15,16 @@ public final class SendMessageCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
         if (args.size() == 0) {
-            CommandHandler.sendMessage(null, translate("commands.sendMessage.usage"));
+            CommandHandler.sendMessage(null, translate(sender, "commands.sendMessage.usage"));
             return;
         }
 
         String message = String.join(" ", args);
         CommandHandler.sendMessage(targetPlayer, message);
-        CommandHandler.sendMessage(sender, translate("commands.sendMessage.success"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.sendMessage.success"));
     }
 }

src/main/java/emu/grasscutter/command/commands/SetFetterLevelCommand.java

@@ -18,19 +18,19 @@ public final class SetFetterLevelCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         if (args.size() != 1) {
-            CommandHandler.sendMessage(sender, translate("commands.setFetterLevel.usage"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setFetterLevel.usage"));
             return;
         }
 
         try {
             int fetterLevel = Integer.parseInt(args.get(0));
             if (fetterLevel < 0 || fetterLevel > 10) {
-                CommandHandler.sendMessage(sender, translate("commands.setFetterLevel.range_error"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.setFetterLevel.range_error"));
                 return;
             }
             Avatar avatar = targetPlayer.getTeamManager().getCurrentAvatarEntity().getAvatar();
@@ -42,9 +42,9 @@ public final class SetFetterLevelCommand implements CommandHandler {
 		    avatar.save();
 		
 		    targetPlayer.sendPacket(new PacketAvatarFetterDataNotify(avatar));
-            CommandHandler.sendMessage(sender, translate("commands.setFetterLevel.success", fetterLevel));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setFetterLevel.success", fetterLevel));
         } catch (NumberFormatException ignored) {
-            CommandHandler.sendMessage(sender, translate("commands.setFetterLevel.level_error"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setFetterLevel.level_error"));
         }
     }
     

src/main/java/emu/grasscutter/command/commands/SetStatsCommand.java

@@ -175,13 +175,13 @@ public final class SetStatsCommand implements CommandHandler {
 
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
-        String syntax = sender == null ? translate("commands.setStats.usage_console") : translate("commands.setStats.usage_ingame");
-        String usage = syntax + translate("commands.setStats.help_message");
+        String syntax = sender == null ? translate(sender, "commands.setStats.usage_console") : translate(sender, "commands.setStats.usage_ingame");
+        String usage = syntax + translate(sender, "commands.setStats.help_message");
         String statStr;
         String valueStr;
 
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
@@ -203,7 +203,7 @@ public final class SetStatsCommand implements CommandHandler {
                 value = Float.parseFloat(valueStr);
             }
         } catch (NumberFormatException ignored) {
-            CommandHandler.sendMessage(sender, translate("commands.setStats.value_error"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setStats.value_error"));
             return;
         }
 
@@ -217,10 +217,10 @@ public final class SetStatsCommand implements CommandHandler {
                 valueStr = String.format("%.0f", value);
             }
             if (targetPlayer == sender) {
-                CommandHandler.sendMessage(sender, translate("commands.setStats.set_self", stat.name, valueStr));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.setStats.set_self", stat.name, valueStr));
             } else {
                 String uidStr = targetPlayer.getAccount().getId();
-                CommandHandler.sendMessage(sender, translate("commands.setStats.set_self", stat.name, uidStr, valueStr));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.setStats.set_self", stat.name, uidStr, valueStr));
             }
         } else {
             CommandHandler.sendMessage(sender, usage);

src/main/java/emu/grasscutter/command/commands/SetWorldLevelCommand.java

@@ -16,19 +16,19 @@ public final class SetWorldLevelCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         if (args.size() < 1) {
-            CommandHandler.sendMessage(sender, translate("commands.setWorldLevel.usage"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setWorldLevel.usage"));
             return;
         }
 
         try {
             int level = Integer.parseInt(args.get(0));
             if (level > 8 || level < 0) {
-                CommandHandler.sendMessage(sender, translate("commands.setWorldLevel.value_error"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.setWorldLevel.value_error"));
                 return;
             }
 
@@ -36,9 +36,9 @@ public final class SetWorldLevelCommand implements CommandHandler {
             targetPlayer.getWorld().setWorldLevel(level);
             targetPlayer.setWorldLevel(level);
 
-            CommandHandler.sendMessage(sender, translate("commands.setWorldLevel.success", Integer.toString(level)));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.setWorldLevel.success", Integer.toString(level)));
         } catch (NumberFormatException ignored) {
-            CommandHandler.sendMessage(null, translate("commands.setWorldLevel.invalid_world_level"));
+            CommandHandler.sendMessage(null, translate(sender, "commands.setWorldLevel.invalid_world_level"));
         }
     }
 }

src/main/java/emu/grasscutter/command/commands/SpawnCommand.java

@@ -28,7 +28,7 @@ public final class SpawnCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
@@ -40,23 +40,23 @@ public final class SpawnCommand implements CommandHandler {
                 try {
                     level = Integer.parseInt(args.get(2));
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.execution.argument_error"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.execution.argument_error"));
                 }  // Fallthrough
             case 2:
                 try {
                     amount = Integer.parseInt(args.get(1));
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.generic.invalid.amount"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.amount"));
                 }  // Fallthrough
             case 1:
                 try {
                     id = Integer.parseInt(args.get(0));
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.generic.invalid.entityId"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.entityId"));
                 }
                 break;
             default:
-                CommandHandler.sendMessage(sender, translate("commands.spawn.usage"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.spawn.usage"));
                 return;
         }
 
@@ -64,7 +64,7 @@ public final class SpawnCommand implements CommandHandler {
         GadgetData gadgetData = GameData.getGadgetDataMap().get(id);
         ItemData itemData = GameData.getItemDataMap().get(id);
         if (monsterData == null && gadgetData == null && itemData == null) {
-            CommandHandler.sendMessage(sender, translate("commands.generic.invalid.entityId"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.generic.invalid.entityId"));
             return;
         }
         Scene scene = targetPlayer.getScene();
@@ -100,7 +100,7 @@ public final class SpawnCommand implements CommandHandler {
 
             scene.addEntity(entity);
         }
-        CommandHandler.sendMessage(sender, translate("commands.spawn.success", Integer.toString(amount), Integer.toString(id)));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.spawn.success", Integer.toString(amount), Integer.toString(id)));
     }
 
     private Position GetRandomPositionInCircle(Position origin, double radius){

src/main/java/emu/grasscutter/command/commands/StopCommand.java

@@ -14,9 +14,9 @@ public final class StopCommand implements CommandHandler {
 
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
-        CommandHandler.sendMessage(null, translate("commands.stop.success"));
+        CommandHandler.sendMessage(null, translate(sender, "commands.stop.success"));
         for (Player p : Grasscutter.getGameServer().getPlayers().values()) {
-            CommandHandler.sendMessage(p, translate("commands.stop.success"));
+            CommandHandler.sendMessage(p, translate(sender, "commands.stop.success"));
         }
 
         System.exit(1000);

src/main/java/emu/grasscutter/command/commands/TalentCommand.java

@@ -19,7 +19,7 @@ public final class TalentCommand implements CommandHandler {
     private void setTalentLevel(Player sender, Player player, Avatar avatar, int talentId, int talentLevel) {
         int oldLevel = avatar.getSkillLevelMap().get(talentId);
         if (talentLevel < 0 || talentLevel > 15) {
-            CommandHandler.sendMessage(sender, translate("commands.talent.lower_16"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.talent.lower_16"));
             return;
         }
 
@@ -40,20 +40,20 @@ public final class TalentCommand implements CommandHandler {
         } else if (talentId == depot.getEnergySkill()) {
             successMessage = "commands.talent.set_q";
         }
-        CommandHandler.sendMessage(sender, translate(successMessage, talentLevel));
+        CommandHandler.sendMessage(sender, translate(sender, successMessage, talentLevel));
     }
 
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
         if (args.size() < 1){
-            CommandHandler.sendMessage(sender, translate("commands.talent.usage_1"));
-            CommandHandler.sendMessage(sender, translate("commands.talent.usage_2"));
-            CommandHandler.sendMessage(sender, translate("commands.talent.usage_3"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_1"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_2"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_3"));
             return;
         }
 
@@ -62,15 +62,15 @@ public final class TalentCommand implements CommandHandler {
         String cmdSwitch = args.get(0);
         switch (cmdSwitch) {
             default -> {
-                CommandHandler.sendMessage(sender, translate("commands.talent.usage_1"));
-                CommandHandler.sendMessage(sender, translate("commands.talent.usage_2"));
-                CommandHandler.sendMessage(sender, translate("commands.talent.usage_3"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_1"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_2"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_3"));
                 return;
             }
             case "set" -> {
                 if (args.size() < 3) {
-                    CommandHandler.sendMessage(sender, translate("commands.talent.usage_1"));
-                    CommandHandler.sendMessage(sender, translate("commands.talent.usage_3"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_1"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_3"));
                     return;
                 }
                 try {
@@ -78,13 +78,13 @@ public final class TalentCommand implements CommandHandler {
                     int newLevel = Integer.parseInt(args.get(2));
                     setTalentLevel(sender, targetPlayer, avatar, skillId, newLevel);
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.talent.invalid_skill_id"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.talent.invalid_skill_id"));
                     return;
                 }
             }
             case "n", "e", "q" -> {
                 if (args.size() < 2) {
-                    CommandHandler.sendMessage(sender, translate("commands.talent.usage_2"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.talent.usage_2"));
                     return;
                 }
                 AvatarSkillDepotData SkillDepot = avatar.getData().getSkillDepot();
@@ -97,7 +97,7 @@ public final class TalentCommand implements CommandHandler {
                     int newLevel = Integer.parseInt(args.get(1));
                     setTalentLevel(sender, targetPlayer, avatar, skillId, newLevel);
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.talent.invalid_level"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.talent.invalid_level"));
                     return;
                 }
             }
@@ -105,9 +105,9 @@ public final class TalentCommand implements CommandHandler {
                 int skillIdNorAtk = avatar.getData().getSkillDepot().getSkills().get(0);
                 int skillIdE = avatar.getData().getSkillDepot().getSkills().get(1);
                 int skillIdQ = avatar.getData().getSkillDepot().getEnergySkill();
-                CommandHandler.sendMessage(sender, translate("commands.talent.normal_attack_id", Integer.toString(skillIdNorAtk)));
-                CommandHandler.sendMessage(sender, translate("commands.talent.e_skill_id", Integer.toString(skillIdE)));
-                CommandHandler.sendMessage(sender, translate("commands.talent.q_skill_id", Integer.toString(skillIdQ)));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.normal_attack_id", Integer.toString(skillIdNorAtk)));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.e_skill_id", Integer.toString(skillIdE)));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.talent.q_skill_id", Integer.toString(skillIdQ)));
             }
         }
     }

src/main/java/emu/grasscutter/command/commands/TeleportAllCommand.java

@@ -16,12 +16,12 @@ public final class TeleportAllCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
         
         if (!targetPlayer.getWorld().isMultiplayer()) {
-            CommandHandler.sendMessage(sender, translate("commands.teleportAll.error"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.teleportAll.error"));
             return;
         }
         
@@ -33,6 +33,6 @@ public final class TeleportAllCommand implements CommandHandler {
             player.getWorld().transferPlayerToScene(player, targetPlayer.getSceneId(), pos);
         }
         
-        CommandHandler.sendMessage(sender, translate("commands.teleportAll.success"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.teleportAll.success"));
     }
 }

src/main/java/emu/grasscutter/command/commands/TeleportCommand.java

@@ -27,7 +27,7 @@ public final class TeleportCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
@@ -42,7 +42,7 @@ public final class TeleportCommand implements CommandHandler {
                 try {
                     sceneId = Integer.parseInt(args.get(3));
                 }catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.execution.argument_error"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.execution.argument_error"));
                 }  // Fallthrough
             case 3:
                 try {
@@ -50,20 +50,20 @@ public final class TeleportCommand implements CommandHandler {
                     y = parseRelative(args.get(1), y);
                     z = parseRelative(args.get(2), z);
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.teleport.invalid_position"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.teleport.invalid_position"));
                 }
                 break;
             default:
-                CommandHandler.sendMessage(sender, translate("commands.teleport.usage"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.teleport.usage"));
                 return;
         }
 
         Position target_pos = new Position(x, y, z);
         boolean result = targetPlayer.getWorld().transferPlayerToScene(targetPlayer, sceneId, target_pos);
         if (!result) {
-            CommandHandler.sendMessage(sender, translate("commands.teleport.invalid_position"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.teleport.invalid_position"));
         } else {
-            CommandHandler.sendMessage(sender, translate("commands.teleport.success", 
+            CommandHandler.sendMessage(sender, translate(sender, "commands.teleport.success", 
                     targetPlayer.getNickname(), Float.toString(x), Float.toString(y), 
                     Float.toString(z), Integer.toString(sceneId))
             );

src/main/java/emu/grasscutter/command/commands/UnlockTowerCommand.java

@@ -21,7 +21,7 @@ public class UnlockTowerCommand implements CommandHandler {
         unlockFloor(sender, sender.getServer().getTowerScheduleManager()
                 .getScheduleFloors());
 
-        CommandHandler.sendMessage(sender, translate("commands.unlocktower.success"));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.unlocktower.success"));
     }
 
     public void unlockFloor(Player player, List<Integer> floors){

src/main/java/emu/grasscutter/command/commands/WeatherCommand.java

@@ -17,7 +17,7 @@ public final class WeatherCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (targetPlayer == null) {
-            CommandHandler.sendMessage(sender, translate("commands.execution.need_target"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.execution.need_target"));
             return;
         }
 
@@ -28,17 +28,17 @@ public final class WeatherCommand implements CommandHandler {
                 try {
                     climateId = Integer.parseInt(args.get(1));
                 } catch (NumberFormatException ignored) {
-                        CommandHandler.sendMessage(sender, translate("commands.weather.invalid_id"));
+                        CommandHandler.sendMessage(sender, translate(sender, "commands.weather.invalid_id"));
                 }
             case 1:
                 try {
                     weatherId = Integer.parseInt(args.get(0));
                 } catch (NumberFormatException ignored) {
-                    CommandHandler.sendMessage(sender, translate("commands.weather.invalid_id"));
+                    CommandHandler.sendMessage(sender, translate(sender, "commands.weather.invalid_id"));
                 }
                 break;
             default:
-                CommandHandler.sendMessage(sender, translate("commands.weather.usage"));
+                CommandHandler.sendMessage(sender, translate(sender, "commands.weather.usage"));
                 return;
         }
 
@@ -47,6 +47,6 @@ public final class WeatherCommand implements CommandHandler {
         targetPlayer.getScene().setWeather(weatherId);
         targetPlayer.getScene().setClimate(climate);
         targetPlayer.getScene().broadcastPacket(new PacketSceneAreaWeatherNotify(targetPlayer));
-        CommandHandler.sendMessage(sender, translate("commands.weather.success", Integer.toString(weatherId), Integer.toString(climateId)));
+        CommandHandler.sendMessage(sender, translate(sender, "commands.weather.success", Integer.toString(weatherId), Integer.toString(climateId)));
     }
 }

src/main/java/emu/grasscutter/game/Account.java

@@ -8,6 +8,7 @@ import emu.grasscutter.utils.Utils;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 
 import org.bson.Document;
 
@@ -28,10 +29,12 @@ public class Account {
 	private String token;
 	private String sessionKey; // Session token for dispatch server
 	private List<String> permissions;
+    private Locale locale;
 	
 	@Deprecated
 	public Account() {
 		this.permissions = new ArrayList<>();
+        this.locale = Grasscutter.getConfig().LocaleLanguage;
 	}
 
 	public String getId() {
@@ -96,6 +99,14 @@ public class Account {
 		return this.sessionKey;
 	}
 
+    public Locale getLocale() {
+        return locale;
+    }
+
+    public void setLocale(Locale locale) {
+        this.locale = locale;
+    }
+
 	/**
 	 * The collection of a player's permissions.
 	 */
@@ -166,5 +177,10 @@ public class Account {
 		if (!document.containsKey("permissions")) {
 			this.addPermission("*");
 		}
+
+        // Set account default language as server default language
+        if (!document.containsKey("locale")) {
+            this.locale = Grasscutter.getConfig().LocaleLanguage;
+        }
 	}
 }

src/main/java/emu/grasscutter/utils/Language.java

@@ -3,6 +3,8 @@ package emu.grasscutter.utils;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import emu.grasscutter.Grasscutter;
+import emu.grasscutter.game.Account;
+import emu.grasscutter.game.player.Player;
 
 import javax.annotation.Nullable;
 import java.io.InputStream;
@@ -11,6 +13,7 @@ import java.util.Map;
 
 public final class Language {
     private final JsonObject languageData;
+    private final String languageCode;
     private final Map<String, String> cachedTranslations = new ConcurrentHashMap<>();
     private static final Map<String, Language> cachedLanguages = new ConcurrentHashMap<>();
 
@@ -24,8 +27,21 @@ public final class Language {
             return cachedLanguages.get(langCode);
         }
 
-        var languageInst = new Language(langCode + ".json", Utils.getLanguageCode(Grasscutter.getConfig().DefaultLanguage) + ".json");
+        var fallbackLanguageCode = Utils.getLanguageCode(Grasscutter.getConfig().DefaultLanguage);
+        var descripter = getLanguageFileStreamDescripter(langCode, fallbackLanguageCode);
+        var actualLanguageCode = descripter.getLanguageCode();
+
+        Language languageInst = null;
+
+        if (descripter.getLanguageFile() != null) {
+            languageInst = new Language(descripter);
+            cachedLanguages.put(actualLanguageCode, languageInst);
+        }
+        else {
+            languageInst = cachedLanguages.get(actualLanguageCode);
             cachedLanguages.put(langCode, languageInst);
+        }
+
         return languageInst;
     }
 
@@ -46,33 +62,89 @@ public final class Language {
         }
     }
 
+    /**
+     * Returns the translated value from the key while substituting arguments.
+     * @param player Target player
+     * @param key The key of the translated value to return.
+     * @param args The arguments to substitute.
+     * @return A translated value with arguments substituted.
+     */
+    public static String translate(Player player, String key, Object... args) {
+        if (player == null) {
+            return translate(key, args);
+        }
+
+        var langCode = Utils.getLanguageCode(player.getAccount().getLocale());
+        String translated = Grasscutter.getLanguage(langCode).get(key);
+        
+        try {
+            return translated.formatted(args);
+        } catch (Exception exception) {
+            Grasscutter.getLogger().error("Failed to format string: " + key, exception);
+            return translated;
+        }
+    }
+
+    /**
+     * get language code
+     */
+    public String getLanguageCode() {
+        return languageCode;
+    }
+
     /**
      * Reads a file and creates a language instance.
-     * @param fileName The name of the language file.
-     * @param fallback The name of the fallback language file.
      */
-    private Language(String fileName, String fallback) {
+    private Language(InternalLanguageFileStreamDescripter descripter) {
         @Nullable JsonObject languageData = null;
+        languageCode = descripter.getLanguageCode();
+        
+        try {
+            languageData = Grasscutter.getGsonFactory().fromJson(Utils.readFromInputStream(descripter.getLanguageFile()), JsonObject.class);
+        } catch (Exception exception) {
+            Grasscutter.getLogger().warn("Failed to load language file: " + descripter.getLanguageCode(), exception);
+        }
+        
+        this.languageData = languageData;
+    }
+
+    /**
+     * create a InternalLanguageFileStreamDescripter
+     * @param languageCode The name of the language code.
+     * @param fallbackLanguageCode The name of the fallback language code.
+     */
+    private static InternalLanguageFileStreamDescripter getLanguageFileStreamDescripter(String languageCode, String fallbackLanguageCode) {
+        var fileName = languageCode + ".json";
+        var fallback = fallbackLanguageCode + ".json";
 
+        String actualLanguageCode = languageCode;
+        if (cachedLanguages.containsKey(actualLanguageCode)) {
+            return new InternalLanguageFileStreamDescripter(actualLanguageCode, null);
+        }
         InputStream file = Grasscutter.class.getResourceAsStream("/languages/" + fileName);
+
         if (file == null) { // Provided fallback language.
+            actualLanguageCode = fallbackLanguageCode;
+            if (cachedLanguages.containsKey(actualLanguageCode)) {
+                return new InternalLanguageFileStreamDescripter(actualLanguageCode, null);
+            }
             file = Grasscutter.class.getResourceAsStream("/languages/" + fallback);
             Grasscutter.getLogger().warn("Failed to load language file: " + fileName + ", falling back to: " + fallback);
         }
+
         if(file == null) { // Fallback the fallback language.
+            actualLanguageCode = "en-US";
+            if (cachedLanguages.containsKey(actualLanguageCode)) {
+                return new InternalLanguageFileStreamDescripter(actualLanguageCode, null);
+            }
             file = Grasscutter.class.getResourceAsStream("/languages/en-US.json");
             Grasscutter.getLogger().warn("Failed to load language file: " + fallback + ", falling back to: en-US.json");
         }
+
         if(file == null)
             throw new RuntimeException("Unable to load the primary, fallback, and 'en-US' language files.");
 
-        try {
-            languageData = Grasscutter.getGsonFactory().fromJson(Utils.readFromInputStream(file), JsonObject.class);
-        } catch (Exception exception) {
-            Grasscutter.getLogger().warn("Failed to load language file: " + fileName, exception);
-        }
-        
-        this.languageData = languageData;
+        return new InternalLanguageFileStreamDescripter(actualLanguageCode, file);
     }
 
     /**
@@ -107,4 +179,22 @@ public final class Language {
         
         this.cachedTranslations.put(key, result); return result;
     }
+
+    private static class InternalLanguageFileStreamDescripter {
+        private String languageCode;
+        private InputStream languageFile;
+
+        public InternalLanguageFileStreamDescripter(String languageCode, InputStream languageFile) {
+            this.languageCode = languageCode;
+            this.languageFile = languageFile;
+        }
+
+        public String getLanguageCode() {
+            return languageCode;
+        }
+
+        public InputStream getLanguageFile() {
+            return languageFile;
+        }
+    }
 }

src/main/resources/languages/en-US.json

@@ -188,6 +188,11 @@
       "success": "Killed %s's current character.",
       "description": "Kills the players current character"
     },
+    "language": {
+      "current_language": "current language is %s",
+      "language_changed": "language changed to %s",
+      "description": "display or change current language"
+    },
     "list": {
       "success": "There are %s player(s) online:",
       "description": "List online players"

src/main/resources/languages/zh-CN.json

@@ -188,6 +188,11 @@
       "success": "已杀死 %s 当前角色。",
       "description": "杀死当前角色"
     },
+    "language": {
+      "current_language": "当前语言是: %s",
+      "language_changed": "语言切换至: %s",
+      "description": "显示或切换当前语言"
+    },
     "list": {
       "success": "目前在线人数：%s",
       "description": "查看所有玩家"