I agree with Ali. The [[Encyclopaedia of Islam] states that N. Sims.Williams' researches partly support the old claims of Enoki, that the Bactrians indeed used Bactrian. However, they also reveal that Bactrian was not the native tongue of the Hephthalites - though still pointing to the theoriy that their native tongue was an East Iranian language, infiltrated with many Turkic and/or Mongolian words.