Kathyra has been under Corvantine rule for several centuries. It was conquered before Varestia was, and was partially colonized by Corvantines, thus it never faced the strife that Varestia did.
Though it has been under Corvantine dominion for centuries, parts of Kathyra still retain their native language and culture.
When Lizanne went undercover as Krista in the Artonin household, Landgrave Artonin noted that she was very pale for being from Corvus. Lizanne told him that her family is from "northern stock", meaning Kathyran.
One of the languages spoken in Kathyra is Selvurin. It is an older tongue that was widely spoken in the north until Varsil became the dominant tongue.