I guess it really depends on the company culture, and one shouldn't over-generalize. I have non-French colleagues who don't speak French (and made barely any progress from their French lessons, but hey it's clearly not their priority ;) and are just fine. But where I work everyone naturally switch to English as soon as there's a non-French speaker in the room.

So my advice to new comers would be to pay attention to this when you visit for interviews. Do you feel reluctance, are people hesitant and searching for words when speaking English? Could be a sign they're not used to it. If they speak casually OTOH (even with strong accent and the odd mistakes) it's likely they're used to it: good.