I found an application that supports addition of Arabic locales in the Play store. It works to change most of the menus, etc. to Arabic and other languages. I tested on CM9 ICS, and it worked to quickly change most items to Arabic. However, this solution didn't work on any non-CM roms that I tried.:
With CM9, this, and the other link I mentioned earlier, you'll be closer to full Arabic.
I know you asked about non-CM roms, but this was the closest to full solution that I could find.
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