Belgian keyboards are now properly supported by xorg window manager, but neither by xsun nor in console mode. You will find below how to solve this problem.
This works only with the original release on Solaris 10 (january 2005) old_bekbd10.tgz
This works with the newer releases of Solaris 10 including patch 118860 (usbkbm) (should also work with unpatched systems) bekbd10.tgz (extract with gtar -zxvf) or bekbd10.ar (extract with tar xvf)
If you need the keyboard files for another version of Solaris x86, contact me