Try this :
- Close Windows Live Messenger
- Open "Start", "Run" and write regedit.
- Go to : HKEY_USERS\[your user number]\SOFTWARE\Patchou\Messenger Plus! Live and find the key named "LanguageFile", right clic and "Modify" and change "Lng_Arabic.ini" into "Lng_Default.ini" or another language.
Try to re-install MPL and tell us if it works