SpigotCore_Main/src/de/steamwar/message/Message.java

@@ -82,7 +82,7 @@ public class Message {
     }
 
     private Locale getLocale(Player player){
-        return SteamwarUser.get(player).getLocale();
+        return SteamwarUser.get(player.getUniqueId()).getLocale();
     }
 
     /* Send a message to one player */