Meshchera language
Meshchera is an extinct Uralic language. It was spoken around the left bank of the Middle Oka. Meshchera was either a Mordvinic or a Permic language. Pauli Rahkonen has suggested on the basis of toponymic evidence that it was a Permic or closely related language, though Rahkonen's theory has been rejected by other researchers such as Vladimir Napolskikh. Some Meshchera speaking people may have assimilated into the Mishar Tatars, though this theory is disputed.
The first Russian written source which mentions the Meshchera language is the Tolkovaya Paleya, from the 13th century. It is also mentioned in several later Russian chronicles from the period before the 16th century, and even later, in one of the letters by Andrey Kurbsky written in the second half of the 16th century, where he claimed the language spoken in the Meshchera region to be Mordvinic.