Idioms don't translate. If you're writing in English, rather than doing what it sounds like you want to do you're better off just writing appropriate English-language dialog for your characters, using whatever English-language colloquialisms suggest the kind of speech you intend. The reader will understand that they're all "really" speaking in colloquial French, it's just all been translated for them.
As for gestures,I can't help with specifics, but I will note that it's probably a good idea not to overdo the stage directions. When an author inserts in too many gestures and motions their characters can end up fidgeting and twitching and grimacing like fools, which usually is not what the writer wanted. Once or twice in a conversation is plenty. Make it count.