Shattered Kingdoms

Since there is a language for demons, couldn't there be a way to make the unclaimed territory the country of the demons and actually make a demon race?

just a suggestion.

My guess would be that you are a rather new player to the game. So, let's start with a welcome.

Now, on the subject:

Unclaimed territories in the world of SKs (they are many not just one area) do not belong to one kingdom, but many places and parts of them have their own history and are related to various historical parts of the world of SKs. Some of them may even be related to clans, others like the Outer Planes are a strange other land on their own.

Just seek for resources in the game, and you will soon come to understand why your idea is not too valid.