Sorry to have let this slip earlier, but ADA roughly T, @Verand first posted on the WIP thread. It was the beginning of a long track record of thoughtful questions and encouraging comment. Thanks @Verand for being part of this community!
It doesn’t have to be either; the option you later describe as “we want to be good neighbors/survive against all the invading magic vampires” can work without a cosmopolitan ideology.
But homelander ideologies have languages or families of languages close to their core. You’d not be able to be strongly homelander and have a single state where both Shayardenes and Whends feel equally at home. In a homelander realm, someone’s language and culture is getting privileged.
Different homelander realms can rub along just fine. You could have a close alliance between your Shayardene domain and Wiendish neighbors. (As long as the borders fall out in a way that doesn’t leave you poised to fight over contested territory like Steswick.) But if you want the neighboring Wiends as subjects rather than allies, you’ll either need to limit your homelanderishness or bring them in on a second-class basis.
No, it’s because one of the primary Seracca dialects involves a phoneme of a light rattle in the back of the throat that’s I’m representing with a double-c. It’s not hard enough to earn a double-k in transliteration.
A century ago the traditionalists weren’t an organized faction hostile to loyalists the way they are today. The de Bors Archons were well placed to keep order at the time.
This was a misunderstanding, I’m afraid 
“Desert” and “plains” are not mutually exclusive descriptions. The Abhuman continent has plenty of semi-arid savannah between the harshest deserts on the Shayard border and the jungles of the far south.