I don't remember if I've seen this mentioned anywhere, but you can listen to an interview in french (and english) here by Charles Delaunay that isn't included on any CD's. Benny tries to speak some french, then Charles Delaunay mentions Django is going to appear as a guest on one of Benny's concerts or something, to which Benny exclaims that it was supposed to be a secret. I'm guessing Django then says he and Benny met at the 400 club (New York City) and after that Eartha Kitt speaks in french. (singer, Catwoman, actress....)
Django's "Oui" sounds more like "Wei", a translation would be nice!