blue with the publication of rasputin must die from paizo, not to mention the fact that mulhorandi and thus Thay, have connections to Earth. In rasputin the characters go from golarion to 1918 russia to kill Rasputin, also their are zombies and animated tanks and a headless horsemen and it is all crazy awesome! with Mulhorandi, and their succusors like thay, IIRC they are -explictly- stated to be ancient egyptians taken from earth to the realms. I am sure I can find more examples.
So with these sort of connections, and I am sure that there is more, perhaps earth characters can have common? since every other realm -including lands that don't have common- have common; i think it would make sense for common to be allowed for Gothic Earth PCs.