Anouar I got this:
1) LANG=ar_FOO in /etc/init.d/gdm. FOO is for EG BH TN etc...
2) dpkg-reconfigure locales
Maybe it helps, no idea if it works for setting up the local for distribution but you have a file and some commands try your best ;) I got also the tip of mailing Gnoppix project, and Debian...
yours Arafat