If you
search for lng_arabic.ini on the forums you'll find several threads with this exact same problem. It is an old problem which popped up lately.
There is no real fix yet. The cause is still unknown.
(changing a specific registry key, as suggested here, is not going to work as you can read here why.)
However, what you maybe could try is to:
1) First reboot PC
2) Then, manually remove the existing languages files in the already installed Plus! directory (usually something like "C:\Program Files\Messenger Plus! Live\Languages").
3) After that, redownload the
latest Messenger Plus! setup and save it to your hard disk.
4) Then start the just saved setup.
Report back if this fixed anything...