Ruanruan

Ruanruan (; also called Rouran) is an extinct language of Mongolia and northern China. It was spoken in the Rouran Khaganate from the 4th to the 6th centuries CE. It is possibly Altaic or Sino–Tibetan.
Some say Ruan-ruan may be a Yeniseian language, a possible Sino-Tibetan language. 
In 2018, "Brāhmī Bugut" and "Khüis Tolgoi" inscriptions suggest that the Ruan-ruan language was a Mongolic language, close to Middle Mongolian.