There's a healthy number of startups in Paris where English is the working language. It's true that day to day life may be more challenging without speaking any French, but probably less so in Paris than elsewhere
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.