Feallan said:
I'm 99% sure there is only one French dub and it was made in 1977.
https://www.youtube.com/watch?v=GUZk_Bk0lTM
https://www.youtube.com/watch?v=-wePinaPP28
The guy, who dubbed Vader in Star Wars (ESB and ROTJ had a different actor) is François Chaumette.
That is correct. When the Special editions came out, they just hired different actors to fill in the changed/new parts. They left the rest of the dubs alone.