Bactrian language
According to the "Beishi", describing the situation in the first half of the 6th century CE around the time Song Yun visited Central Asia, the language of the Hephthalites was different from that of the Ruanruan, Gaoju or other tribes of Central Asia, but that probably reflects their acculturation and adoption of the Bactrian language since their arrival in Bactria in the 4th century CE. The "Liangshu" and "Liang Zhigongtu" do explain that the Hephthalites originally had no written language and adopted the "hu" (local, "Barbarian") alphabet, in this case, the Bactrian script.