And "Hamburger" is a person from Hamburg, where the "u" is pronounced ⟨u⟩ like in engl. "boot". (The same pronounciation btw. as in the German surname "Trump".)
Ironically, Frankfurter in Germany refers to another kind of sausage made of beef (originally invented to circumvent jewish food laws against consuming pork), which has absolutely nothing to do with Wiener (or vienna "Frankfurter")
Even weirder fact: at the time it was not legal to mix pork and beef in Germany because there were different trade licenses for both meet types. Supposedly mixing in beef was thus first done in Vienna.
The dominant Portuguese manufacturer Nobre has adopted the Austrian notation.