Common

This language is magically universal. The language, once learned, can be taken to any place with another version of Common and be understood. The miraculous magic surrounding this language in Gether is that people that know a “common” language from a different universe can still understand one another. From out here in the real world, it would be like three people that spoke different languages, would all instantly understand one another if they were dropped into Gether, and would understand others from other worlds if they had completely different sets of “Common”. The fact that they are all speaking different language is only confusing to people if they know for a fact another person didn’t know their language until arriving as Skyfell. Otherwise everyone around just hears the same thing or sees the same characters on a written page when the two linguists speak or write. This magical linguistic trend holds true of any of the ancestral languages. Dwarves from different worlds understand one another. Elves, if their world has a commonly shared language, will understand one another when they arrive in Gether.
This concept of Common is included in the Gether Guide to Languages on DrivethruRPG:
https://www.drivethrurpg.com/product/328473/Gether-Guide-To-Languages