I don't know about the newer versions of the movies, but I grew up watching the OOT movies in French as much as English (maybe more depending on which channels were playing them) and I remember Vader's voice being excellent! I remember Chico, too. :)
Are there any preservations of the OOT with the French audio track? I'd love to have those, including the version where Chewie is Chico. (instead of just buying random old VHS tapes on eBay or something...)