Classification
Arab scholars of the Middle Ages classified Khazar as similar to, yet distinct from, the type of Turkic spoken by other Turks with whom they were familiar, such as the Oghuz Turks. They noted, however, that both the Khazar tongue and the more common forms of Turkic were widely spoken in Khazaria.
The consensus among scholars had long been and still is that the Khazars spoke an Oghuric Turkic language similar to Chuvash, Hunnish, Turkic Avar and Volga-Bulgarian, possibly influenced by Old Turkic and Uyghur influences, as was stated by Al-Istakhri "the language of Bulgars resembles the language of Khazars". The Ogur languages are characterized by sound correspondences such as Oguric r versus Common Turkic z and Oguric l versus Common Turkic ลก.
The capital of the Khazars was named Sarkel, which points markedly towards an Oghuric language, as the etymon connected to *sar- means 'white' only in Chuvash, while 'yellow' in the Common Turkic languages. Also, the corresponding etymon for *-kel is only found in Chuvash (meaning 'house, shelter') and is not extant in the Oghuzic branch of the language family.
The Oghuric origin hypothesis for the Khazar language has been disputed since the 1990s, by authors suggesting that the Khazar language was a standard, "Shaz"-style Common Turkic language.
Read more about this topic: Khazar Language