I have two characters who are in French-speaking Africa who dialogue quite a bit with the MC who is North American. This means their first language is their West African language, the second (in which they are very fluent) is French, and English is a third language. They are quite proficient in English (say B1 or B2 on the International scale). I've written dozens of scenes with them, but in the second draft I want to focus on making their speech believable. So far, in the first draft, I've had them drop in french words parfois, being careful not to do it too much as it get obnoxious. Also, not relying too much on phrasal verbs, which, it seems, mostly native speakers master. Any other tips for making their French accents believable? Another consideration is that they appear and speak a lot throughout the book, so anything annoying (such as spelling out their diction phonetically "are yu going to..ah..mit with me thes evenING? Or do You av someTHING to do?) won't work. I'm looking for subtlety. Thanks.