We'll try and get this fixed for final.

So to help us out.

Does kbd=be give a French keyboard suitable for Belgium?
Does kbd=be give a Dutch keyboard suitable for Belgium?

What is exactly needed in /etc/defaults/keyboard for you to have Belgian-Dutch and Belguian-French?

XKBMODEL="pc105"
XKBLAYOUT=""
XKBVARIANT=""
XKBOPTIONS="grp:alt_shift_toggle,terminate:ctrl_alt_bksp,grp_led:scroll"

This thread may be closed now.

I installed again logged into the live environment (not using the cli-installer) and everything went smooth from there on.

Sorry for all your trouble.