Hey

The differentiation looks to be a bit arbitrary and, as Peter Heather explains greatly in "Goths And Romans" they weren't divided like that before the interaction with Romans and Huns. Among the IVth and Vth century Goths genetic diversity must have been notable, apparently you became a Goth by serving in the Gothic armies or even by marriage (we have an example of a Greek merchant becoming a Hun this way).

Linguistically, to the eyes of the romanized peoples, the Visigoths, Ostrgoths and Vandals spoke the same language, although there were (probably) regional and national dialects as one can see in the Vandalic pictogram.

If you want any references for further reading just ask and when I am home I can point you to them, but Peter Heather is just excellent 👌🏻