Hi,
I think Debian uses XFree86, not x.org as most other current distros.
So your configuration should be in
/etc/X11/XF86Config-4
You can open it as root in an editor.
There is a section “Inputdevice”.
Have a look if there are special entries.
In my old XF86Config4 I used a year ago it looks like this (german keyboard)
Section “InputDevice”
Identifier “Keyboard1”
Driver “Keyboard”
Option “XkbModel” “pc105”
Option “XkbLayout” “de(nodeadkeys)”
Option “XkbOptions” “”
EndSection
I think you must replace “de” (allemand) with “fr” (francais)?
These entries worked fine with fvwm.
Bien de saluts, Mark