Fix updating join message when not needed (#6312)

Prevents calling setJoinMessage when the message is unchanged causing
Bukkit to no longer send the translation key to the client (nuking
vanilla translation)

Fixes #6307

Author: JRoy

Essentials/src/main/java/com/earth2me/essentials/EssentialsPlayerListener.java

@@ -450,7 +450,10 @@ private void joinFlow(final User user, final long currentTime, final String mess
             effectiveMessage = message;
         }
 
-        joinMessageConsumer.accept(effectiveMessage);
+        // Only change the vanilla join message if it's different to avoid nuking client translation
+        if (effectiveMessage != null && !effectiveMessage.equals(message) || message != null && effectiveMessage == null) {
+            joinMessageConsumer.accept(effectiveMessage);
+        }
 
         ess.runTaskAsynchronously(() -> ess.getServer().getPluginManager().callEvent(new AsyncUserDataLoadEvent(user, effectiveMessage)));