Whatever Remains, However Improbable

First, as we already pointed out the Romans have used the word Germania to designate an area where northern folk lived. To the Romans they would have appeared similar since the Romans judged them by their own looks, language, culture. But would they appear so similar to one another? In other words, there is really nothing to suggest that all the tribes there were similar in all respects – including language. And, even if so, we do not know what that language was.
So here we have Germanic tribes of:

Goths
Vandals
Lombards
Herules
let’s add Franks too.
we had Ariovistus and Veleda and Ganna and Masyus – were these Germanic names? They sound (well, “look and sound”) Slavic or Baltic or maybe Avestani but not Germanic