Napoleon's first language was Italian, and he spoke French with a Corsican accent. France conquered the Corsican Republic in 1768, Napoleon was born in 1769 to a line of minor Italian nobles (not that Italy was an actual thing yet)
TL;Dr he shouldn't have a French accent because he didn't have one
That bothered me severely in the first Wonder Woman movie. Wonder Woman and her actor friend can speak like every language, which is demonstrated on screen, but the Germans speak English. There was not so much German talk in the movie that it could not have been in German.