A number of people have concluded that the Huns spoke a Yeniseian language or even an Iranian language. A study of a Xiongnu graveyard found that nearly half the Y hgs were R and Q (the rest were C), suggesting they descended from a Okunevo or Karasuk people that had absorbed an Altaic population in Mongolia.
It's still impossible to know, but I think it's most likely Turkic. I have a ton of sources, but in the end you have to theorize. Some of the latter findings are what they think was Hunnic script that looks like Turkic.
C, R, and Q are anywhere on the steppe and NE Asia.