problem belgian keyboard mapping ubuntu 12

Hi, i'm using my macbook pro under ubuntu 12.04 for work and i use the apple (non-wireless) keyboard with it. The problem is that it's a belgian one, and some keys do not match to the symbol on my keyboard... It's quites annoying!

I precise that i already tried to configure it in the keyboard options in the system preferences, there is only french (for France) keyboard for mac, not belgian...

Any ideas?