Oh I would be much happier with the world building if instead of Common it was called "Local (insert area)" Pidgin, or something. And everybody can get by with it just fine usually. It is really just the blank wall that is the word Common that bugs me.I wouldn't mind Common so much if it were really a pidgin language, not suitable for much beyond trade.
Common is like the Universal Translator from Star Trek. It makes things easier, and that is fine, I would just rather have someone having done some world building around it so we can have a word that describes the local language so it feels like a place that could exist, you know given magic and monsters and such.
^2