I'm not sure of the realism of this, but I think there's precedent for it in the ancestors of Indo-European (migrations are believed to have happened from the modern Ukraine as far as Spain, Italy, and India). Anyway, given the realism of this NES...
Ancestors of the Dagranites- The Proto-Dagvernian People
The Dagranite language has it's ancestory in eastern Palestine, which in about 10,000 BC was home to the Proto-Dagvernian people. It is believed that some factor pushed them northward, although it's nature is unknown. However, given linguistic similarities, this movement must have happened.
These Proto-Dagvernians would then settle in eastern Anatolia, although a splitoff group colonised the far northern Euphrates (the Proto-Vernians). This movement continued north, where they were displaced by another people, postulated to the ancestors of the Indo-Europeans.
The Proto-Dagrians were not just the Dagrian tribe, but a large ethnic group that existed north of the Ukraine region. Since early times it was recorded that they had great difficulty understanding their southern neighbours, to the point where interaction in practice did not happen.