Since French was a foreign language for the Russian reader, it is arguable that every translation should keep those sentences in French. Yet none does.

To take a famous example, the opening lines of War and Peace in the original are: 'Eh bien, mon prince' followed by long passages in French spoken by Russians as if it were their normal everyday language. the characters in question are aristocrats who converse with one another in French for reasons of fashion and snobbery - something the linking text (in Russia) makes clear   Ironically the discussion is about the possible invasion of Russia by Napoleon and 'toutes les atrocites de cet Antichrist.'  Since French was a foreign language for the Russian reader, it is arguable that every translation  should keep those sentences in French. Yet none does.

 J. Erdal, Ghosting: a double life (2004), 85-6