You raise an interesting point. I mostly answered from the point of view of an engineer, for whom it's not the biggest issue not to speak french. For a founder though it'd make things more complicated. They'd need to have someone close who speaks french, especially since there is a bunch of paperwork to do to start a company here and some physical interactions with french administration where english speaking might not be guaranteed.

They will also be more impressed and glad that some foreigner is trying to create value in their country. I don't think language is really a barrier in this case.

Definitely not a problem with French investors. They're business people who will of course speak English.

The real challenge for a non-French speaking founder would mainly be in dealings with local authorities. You can't expect public servants to speak any English or have any English-translated documentation / forms available.