but people who have lived in several different cultural milieus don't actually usually mix their idioms so freely. What they do is code-switch

you've very neatly put your finger on what used to bother me about the dialogue; I never managed to quite articulate what was annoying me besides "oh my god pick a style of speaking already." Which seemed a bit unfair, as they have lived in all sorts of times and places, and yet it still seemed contrived rather than organic.