Interesting point with adjectives vs nouns.

'a Frenchman' would be more correct than 'a French'. Because French is only an adjective, while American and German are both nouns and adjectives. But Frenchman is not gender neutral like German or American.

Could go with Francophone, but that's any french speaking person so that includes canadians, africans, etc.

And, it would seem to make sense to go with Frank, but the Franks were originally germans, then expanded their territory to include France, and the name stuck there but not in their original territory, so is it really correct to refer to the French as Franks? Since no one does it, I would guess not.