A while ago, I worked with a client who is using Redmine Arabic interface. I found the arabic translation of Redmine very weak. It is missing many translations and miss-translates many others and causes a lot of confusion.
The good news is that I have reviewed Redmine arabization and adjusted the arabic translation to match the majority of arabic speakers in Egypt, the gulf area, and the Middle East. Also, I have fixed many incorrect translations and added missing ones.
The new translation is released with Redmine 2.4.0, and here is the patch that I have submitted.