A lot depends upon where the
boat is flagged. If US flagged, US rules. If French flagged, French rules. It gets exciting if you want to keep a foreign (non EU-flagged) vessel in the EU longer than the permitted period. Things like VAT raise their heads. Words like Schengen come up. If you get
training or certifications here, are they admissible or recognized in France? A
radio license is required in France to operate a
VHF, and a US
license should be acceptable for that. Besides that, a USCG license would probably be worth something. Others may know more about equivalencies, but French websites are full of people concerned about getting fined for being on a boat more than 6 miles from a port if they haven't gotten their "high seas" (hauturier) certificate.
This might be a good place to start:
https://www.mer.gouv.fr/le-permis-pl...ance-moteur#e5