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This chart showing interrelationships among the tongues of Mídhris is old. I do not think I believe it any longer.
Just as languages change, so do the linguistic theories about how those changes have come about.
There is a great deal I need to ponder in terms of tribal migrations, ethnic and linguistic influences, trade, and the sheer matter of politics and economics (the languages of dominant groups end up dominating). At the time of the tales recounted in the Chronicles the primary languages are Standard Mithron, Perrine, Druvic, and Hlvi. Imperial Sivvaron is a foreign tongue and largely lost except in ancient records. Missionaries from the Empire abandoned it quickly in favor of a language "understanded of the people." Since gnords communicate telepathically there is really little sense in postulating a language for them. Besides, they're birds, though certainly not ordinary ones.
I really do enjoy the perversity of having Nivan and Perrine related. The Perrine Isles are far to the south of the Mere and Nivan only survives in areas like the hills above Nialt and Tolvith. How the hell did that happen? It would be a pity to smooth out that anomaly.
The materials from which The Chronicles emerge have developed over four entire decades. I have changed my mind about many things in that time period. It will be interesting to see what emerges as the stories are finalized and published.