Tocharian is an extinct branch of the Indo-European languages spoken in the Tarim Basin, in what is now Xinjiang, China. It is known from manuscripts dating to between the 5th and 8th centuries CE from oasis cities on the northern edge of the basin. These documents are written in two separate languages, known as Tocharian A and Tocharian B. A third Tocharian language, called Tocharian C, is known from a body of loanwords and names found in Prakrit documents.

A bit more detail on the languages:

  • Tocharian A: Also known as East Tocharian or Agnean, this was a more archaic language used as a Buddhist liturgical language
  • Tocharian B: Also known as West Tocharian or Kuchean, this seems to have been the language that was more actively spoken at the time the documents date back to.
  • Tocharian C: Also known as Kroränian, this form of Tocharian is only known from loanwords (particularly to do with taxation and civil administration) and names recorded in otherwise-Prakrit documents found on the southern edge of the basin. These documents date back a little earlier than the Tocharian A and B ones.

It’s thought that Tocharian speakers descended from the Afanasievo Culture of South Siberia (c. 3300–2500 BCE); if so, the Tocharians’ ancestors would have migrated southwards to the Tarim Basin at some later point. The Tocharian branch does seem to have had some unusual (for Indo-European) features that are indicative of heavy influence by Uralic languages, specifically Proto-Samoyedic, and other languages spoken in Siberia. Some of these include the mergers of all Proto-Indo-European’s stop series (voiced, voiceless, aspirated) into just a voiceless series, the almost-wholesale borrowing of a Siberian agglutinative system for marking noun case, and a vowel system basically identical to the Yeniseian language Ket. On the other hand, Tocharian was very conservative in its retention of PIE’s verbal conjugation system. It was a centum language.

It’s also thought that Old Chinese might have borrowed some words from Tocharian, particularly the word for “honey” (*mjit in Old Chinese, *ḿət(ə) in Tocharian).

Tocharian seems to have gone into decline after the migration of Uyghurs into the area after their expulsion from Kyrgyzstan; there exist a number of documents that are translations between Tocharian and Uyghur from around this time, lending credence to the idea that language shift took place. Tocharian was probably extinct by the 10th century CE.