It is always a challenge to make software and computing in general do Arabic (and other languages that are Right to Left and uses variable shape letters). Regarding the internet, I wrote several articles about Arabic on the Internet with a lot of background information, technical challenges, state of the market, and more. As far as Drupal is concerned, you can read my article on the various possible approaches for the Arabization of Drupal. There was an interesting discussion there from various people, including some with Afghani sites. Both Pashtu and Dari use variants of the Arabic script. Later, Egypt's Linux Users Group used Drupal with Arabic and English intermixed. A project for an Drupal Arabic translation was later created. Another good case study is the CSC-SY site going Drupal.