normal user cannot select a language
I installed gutsy i386 d-i 20070823 in Dutch (with English keyboard), and then used Systeem / Beeheer / Language support to add Arabic as a supported language. I left Dutch as the default for sessions and the login screen.
I then created a new user, and logged in as that user using the fast user switching applet. I cannot find in the menus any way to change the language used for this new user. There should be a discoverable way (eg, under System / Preferences) for a user to set their own language.