Achehnese is a language spoken by 2 to 3 million people in Aceh in northern Sumatra, where Banda Aceh was once the capital of an independent Muslim kingdom and a major port of call in the eastern Indian Ocean.
The closest linguistic relatives of Achehnese are not, as one would expect, the other languages on the island of Sumatra, but rather Cham and the Austronesian languages of the distant Vietnam. Why is this the case? Speculation is rampant, but facts are few.
Achehnese has borrowings from Sanskrit, some of which are shared with Cham. There are loanwords from Malay as well, as Malay was used officially in Aceh even during its independence, and remains the national language today, under the name Indonesian.
Formerly written in the Arabic script, Achehnese has had a standard Latin orthography since 1979.
The language has also been called Aceh, Atjeh, Atjehnese and Achinese with ISO 639-2 code ace. Dialects include Banda, Baruh, Bueng, Daja, Pase, Pidie (Pedir, Timu) and Tunong.
Andrew Dalby's Dictionary of Languages