I understand that the French voice actors who dubbed Star Wars were quite famous actors in their own right. Apparently, an article about dubbing the new scenes in the SE was printed in 1997 in "Les Années Laser", a French magazine about home cinema.
There was a history of "who dubbed what and how" and also an interesting statement about the sound of the French LDs being plain stereo and not Dolby Surround because the original 1977 French mix for the movie was only a 2-channel stereo mix due to limitations of French theaters at the time. (Same statement appears on the lddb listing here).