Goes all the way back to at least Proto-Germanic *finnaz for Sami, possibly from "to travel by foot, walk". Not terribly unrealistic given the semi-nomadic lifestyle of Sami, Sami and Suomi might just be the same word via general Uralic relatedness (and sound the same to Germanic ears anyway) also what's now considered Finns was back then a rough assemblage of tribes consisting of multiple Uralic immigration waves known to Swedes as "Forest Finns", as supposed to the herding Finns (ie. nowadays Sami) further north.
Which I guess makes Estonians Swamp Finns (in so far as Finland-Finns aren't claiming that one for themselves with their swamp forests) and Hungarians... Paprika Finns.
Still do, Franken is on the one hand a part of Bavaria very insistent on not actually being Bavarian (and they're right), OTOH a dialect continuum reaching over the Ruhr area up to Flanders and Holland.
Charlemagne was a prince of Austrasia, just another guy in a long dynasty of conquerors but notably the one to conquer Rome (and conversion-by-genocide of the Saxons). Also a lot more Gauls back in the day in France before they went all national state and suppressed minority languages in favour of sounding more Roman.