Since we're on the subject, saying "a French" sounds wrong to me (American native English speaker), even though the same construction is OK for other nationali

Since we're on the subject, saying "a French" sounds wrong to me (American native English speaker), even though the same construction is OK for other nationalities. (E.g. "a German" is OK.) You're better off with "a Frenchman"/"a Frenchwoman" or "a French person".