I don't know. The thing is, even the statement that they use 'common hyur', is if I recall correctly, more accurately using 'the common tongue of the hyur'. It doesn't really say 'the Common Tongue of the Hyur' (emphasis on capitals). It can be anything, the common tongue of the Hyur (implied, the Hyur from Doma), for example.
So, there is that.
So, there is that.
Balmung:Â Suen Shyu