Kharoshti (Bactrian) was the ancient north Afghan language which is a derivative of Aramaic, which in turn is a derivative of Hebrew.  It was unique among the Iranian language in the sense it is written using Greek scripts, a legacy which Alexander the Great had left behind after his victory over Bactrian in the fourth century BC.  Soon after the conquest of Bactria by the nomadic people, Greek was the official language and script for administrative purposes.  It's new rulers (Kushanas) Kujula Kadphises, Vima Takto (Kujula's son), Vima Kadphises continued the usage of Greek script to write the local language.  It is Kanishka who adopted Bactrian as the language on his coins, thus became a cause for Greek language to disappear slowly.  Kanishka introduced the Iranian title, Shaonanoshao - "King of Kings" in place of Greek form Basileos Basileon.  Bactrian emerged as the most important language throughout the Kushana empire at least for six centuries even after the fall of Kushanas.  Certain Brahmi letters seems to have distinguished in the coins of successive rulers.