Hi, I think that I have the same problem that you. I'm also using a fr keyboard.
In fact, I'm using a "Alt + a" binding which is not work anymore and I didn't change my fvwm config file. Besides, I've just realized that my binding is now "Alt+q". Everything happens as if I had a qwerty keyboard. However, I only have this fvwm, everything else still behaves according to my keyboard mapping. Is it the same problem with you ? I don't know where this problem comes from. Any idea ? Thanks, Jean