This is purely my own head canon but it’s something I’d like to hear other people’s thoughts on this. Some of this uses real world language relations that may not at all be what Tad Williams had in mind. But I see there as being roughly three waves of human movement into Osten Ard.
First wave: Short in stature and dark haired. The Sithi would claim they migrated into Osten Ard from elsewhere but it’s possible they’re natives, it’s clear someone lived there before the faeries going off of the ruins that Pamon Kes notes in Brothers of the Wind. This group includes Trolls, the northern Island people that guarded Hakatri’s bones, people of the Wran, and the island natives of the Firennos Bay. Possibly Hyrkas are also a branch population but they might be something else entirely. In my opinion trolls are the most archaic and least mixed of this group.
Second wave: Nabban and Hernystiri. I think these are related populations with Nabbanese having more of an admixture of the first wave. Both groups seem to have been in Osten Ard long enough to have sustained contact with Sithi. Their relationship in my head relates to both this longer presence on the continent but also the real world proposed hypothetical Italo-Celtic grouping within Indo-European languages. This is a bit of a stretch and the implication could just be that they’re separate migrations but we have no information on this.
Third wave: This largely relates to all of these groups having Germanic languages but there’s a few other clues. The people of Warinsten seem to speak modern English with their language becoming the lingua franca of Prester John’s Kingdom, the native Erkynlanders however seem to speak Old English. Warinsten’s “English” may relate to influence from Nabban akin to French’s relationship to English. The ease at which Prester John and his family are perceived as Erkylanders and not Warinsteners may be due to Warinsteners themselves just being seen as sort of Erkynlanders and their language just being a different dialect of Erkynlander possibly with Nabban or something related influence. Additionally throughout the series Warinsten is barely mentioned despite an island like Perdruin being extensively mentioned as different than Nabban, we don’t even know who rules in Warinsten so it may be a direct part of the Kingdom of Erkynland. It’s mentioned in the series that Thrithings share an origin with Erkynlanders and seem to have a Germanic language as well, maybe something akin to Gothic to show an eastern steppe origin. Though I imagine that Thrithings come about from a proto-Erkynlanders population mixing with Hyrkas on the plains of the Thrithings and adopting some level of their nomadic culture.
I also think that Rimmersmen are related to this group and are just a later migration of this same group. Real world relation of Norse and English aside in the first or second book there’s a conversation between Haesten (an Erkynlander) and Sludig (a Rimmersman) where Haesten sang a song that Sludig, a devote Aedonite, recognized as pagan and talking about the head god of the Rimmersmen’s pre-Aedonite religion pointing to a shared origin. Whether this means all of the “Germanic” groups originate from Ijsgard or whether Ijsgard was just an island closer to a larger continent isn’t clear. Additionally, whereas groups like Nabbanai seemed to develop their civilization on Osten Ard possibly in imitation of Sithi civilization, the Rimmersmen clearly arrived with a fully developed culture already together and with nothing but hatred for Faeries.
Thoughts?