Why does his wife have a constipated UK accent?

No idea.

I thought it didn't make any sense that they had their big argument in english, shouting to eachother while speaking french to eachother the rest of the time. For dramatic purposes surely, but still it didn't make any sense. Either they should speak english all the time or french all the time.

But I guess those are complexities that directors have to struggle with.

Perhaps because Jacqueline Bisset is British, no? You didn't expect that trash of a movie to bother to be faithful to the original characters, did you?

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www.1up-games.com Last watched: imdb.to/K4tvL9

When a movie based on a real story changes the characters' names, it means it's not going to show everything exactly how it was (as it was stated in the disclaimer at the beginning). Even if that was wrong, the character's nationality isn't really important.