I want to stress that the Folio Project has little to do with the version I'm currently running. Still, I thought I'd continue developing it in anticipation of the day that I run Greyhawk without a co-DM.
When I first started this project, I decided to tie the various ethnic groups of the Flanaess to pantheons from Deities and Demigods. This action served two purposes. First and foremost, it acted as a historical short-hand for the various cultures. Second, it helped me define the major gods of the setting. My initial ideas looked something like this:
Oeridians: Greek (possibly mixed with Norse)
I imagine that the Baklunish is the weird one on the above list. I see them as various Turkic peoples, but my decision to associate them with the Indian Mythos was based on the Karaks from the 3.5 version of the Wilderlands. I put the Flanae with the Finnish Mythos because according to the map on page six of the Folio they exist in tiny, disconnected pockets across the Flanaess. This made me think of the Finno-Ugric language group in Europe. I'd probably mix in some Slavic stuff, which I imagine would offend both parties, but I know far more about early Russia than I do about Finland. The Oeridians I think are fairly easy to figure out. I thought about making the Great Kingdom be the home of the Greek Pantheon, and the further you get away from there the more Norse the pantheon becomes.
Most Greyhawk fans probably noticed the absence of the Suloise from the above list. They have been the great enigma of the Folio Project. I had based most of my treatment of them off of their desert origins. Perhaps the would be similar to the Phoenicians, and possibly use the Babylonian or Sumerian Mythos so that I could still use DDG. This becomes complicated when one notices that the southern banks of the Nyr Dyv, i.e. Greyhawk, are heavily Suloise. I want Greyhawk and its neighbors to be pseudo-medieval in character. Some may find that a bit boring, but I'm a fan.
It was only when I met with my co-DM that I became aware that their supposed to be pseudo-Norse. This seems to contradict their origins, but it makes sense with their current situation, especially in the case of the Snow Barbarians. I suppose I'll go with that, though it does rob me of the ability to have the Scarlet Brotherhood be Ziggurat building sorcerers obsessed with human sacrifice. More is the pity.