Chittagonian language

Chittagonian, also known by its endonym Chatgaya ( "Chaţgãia") is an Indo-Aryan language spoken in the Chittagong Division in Bangladesh. It is generally considered to be a nonstandard dialect of Bengali because its speakers identify with Bengali culture and Standard Bengali as
literary language, but the two are not mutually intelligible. It is estimated (2009) that Chittagonian has 13–16 million speakers, principally in Bangladesh.
Classification.
Chittagonian is a member of the Bengali-Assamese sub-branch of the Eastern group of Indo-Aryan languages, a branch of the wider Indo-European language family. Its sister languages include Sylheti, Rohingya, Chakma, Assamese, and Bengali. It is derived through an Eastern Middle Indo-Aryan from Old Indo-Aryan, and ultimately from Proto-Indo-European.
Writing system.
Historically Perso-Arabic script was used for the writing system. The Bengali-Assamese script is the most common script used nowadays, although the Arabic script remains in use.