When I saw this film there was only one scene where Piccoli and Bardot speak in French. This happened in their apartment when he was looking at the art book. Please don't tell me I saw some stupid version of the film.
If this was indeed the only scene in French, why did Godard make this decision? I really hope I haven't seen a butchered copy.
I am not sure of it but it seems like the film was completely shot in French and then dubbed in English by the same actors. My DVD contains the French, English and German dub where the English soundtrack indeed switches to the original French recording in the scene you mentioned. Perhaps there was something wrong with the English track and they simply replaced the erroneous part.
That version that you saw was the dubbed version in English. The small scene that you mention is in French because that was cut of the version released originally in the United States, and because of this in the complete version it does not have the a dubbing for it. I recommend everyone to switch to the french track, who is not simply in french since has a lot of talk in English and a little in italian and it uses direct sound. All that Jack Palance speaks in the film is the same in both versions, even so english track loses context of diverse scenes, that they will not count the translation that the assistant in the film makes for michel piccoli, in diverse lines the translation has an modification that it can remember to a proposital effect of the style "lost in translation". all conversations that piccoli and bardot have are in french.
There are also some dialogues, no, rather sentences spoken in German by Fritz Lang.
The language muddle is one of the things that eventually make this movie as interesting as it is, especially if you understand all of the four languages. Then you are always ahead of the protagonists except the girl who translates. However, this can also be very annoying, particularly in the beginning in Cinecittà where everything is translated by the Italian girl at once.