Low Gothic is the common tongue among humans. It is a simplified and modernised form of High Gothic, and despite differences in dialect, is understood universally.
High Gothic is an older form of the Gothic language. Rarely used, it is most often heard among Adepts and members of the Inquisition. The pious tend to learn it as well, as do the overly wealthy. High Gothic is understood by only a handful, and even the handful that speak it only use it as a second language.
Protogothic is a language even older than High Gothic. Spoken by a very rare few, Protogothic is the original form of Gothic, in all it’s convoluted glory.