Do you have corrupted fonts in-game?
If you see squares in the game client language instead of English text then you are missing windows font called Arial Unicode MS. It's a common in all new Mu Online clients so make sure to follow the easy steps listed below.
1. Close game client
2. Navigate to Atlas MU Game Client folder
3. Open Fix Font Folder
4. Right click ARIALUNI.TTF and click Install
5. Alternatively you can copy ARIALUNI.TTF to C:/Windows/Fonts and then start the game.