American and French

Tom, Phillipe, and Freddie are all defined as American but they remain in conversations in French for the entire film. Even though it's primarily because they cast French actors, except for the one playing Freddie, I wonder how they expected the viewer to act around that logic. I accepted it and it didn't distract me, but whenever I'm reminded that these guys are American, I couldn't see the logic to it and wondered why Clement didn't just simply make the characters French as one deviation from the book.