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/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){