The Northwest Sumatran languages are a putative group of languages spoken by the Batak

Batak (Indonesia)

Batak is a collective term used to identify a number of ethnic groups predominantly found in North Sumatra, Indonesia. The term is used to include the Toba, Karo, Pakpak, Simalungun, Angkola and Mandailing, each of which are distinct but related groups with distinct, albeit related, languages and...

 and related peoples in the interior of northern Sumatra

Sumatra

Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

, and by the Nias, Mentawai, etc. on the barrier islands (Simeulue

Simeulue

Simeulue Regency is a regency in the Aceh province of Indonesia. It occupies the whole island of Simeulue , 150 km off the west coast of Sumatra, with a population of 80,279 ....

, Nias

Nias

Nīas is an island off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago, containing the Hinako archipelago....

, and Mentawai Islands

Mentawai Islands

The Mentawai Islands are a chain of about seventy islands and islets off the western coast of Sumatra in Indonesia. Siberut is the largest of the islands. The other major islands are Sipura, North Pagai and South Pagai . The islands lie approximately 150 km off the Sumatran coast, across the...

) off the western coast of Sumatra.

Classification

The languages normally included in North Sumatran are,

• Batak languages
  Batak languages
  The Batak languages are spoken by Batak and Alas people of North Sumatra, Indonesia.Historically they were written using Batak script but the Latin alphabet is now used for most writing....
  
  
• Gayo
  Gayo language
  Gayo Language is the spoken language of about 180,000 people in the mountain region of North Sumatra around Takengon, Gayo Lues, Bener Meriah, Southeast Aceh, Genteng, and Lokop. It is classified as belonging to the Western Malayo-Polynesian branch of the Austronesian languages, but is not closely...
  
  
• Enggano
  Enggano language
  The Enggano language, or Engganese, is the language of Enggano Island off the southwestern coast of Sumatra.Although adjacent to Austronesian languages, Enggano has not been established as Austronesian; it may instead be a language isolate with Austronesian borrowing. Much of the basic vocabulary...
  
  
• Mentawai
  Mentawai language
  The Mentawai language is an Austronesian language, spoken by the Mentawai-people of the Mentawai Islands, West Sumatra. The dialects of the language include: – Silabu, Sipura – Simalegi, Sakalagan, Saumanganja – North Siberut, South Siberut – Taikaku – Pagai....
  
  
• Northern Barrier Islands: Nias
  Nias language
  The Nias language is an Austronesian language spoken on Nias Island and the Batu Islands off the west coast of Sumatra in Indonesia. It belongs to the Northwest Sumatran subgroup which also includes Mentawai and the Batak languages. It had about 770,000 speakers in 2000...
  
  , Sikule, Simeulue

However, a 2008 analysis of the Austronesian Basic Vocabulary Database found no support for a northern Sumatran family. Toba Batak and Gayo were found to fit in different branches of an expanded Malayo-Sumbawan

Malayo-Sumbawan languages

The Malayo-Sumbawan languages are a group of languages identified by Adelaar that unites the Malayic and Chamic languages with the languages of Java and the western Lesser Sunda Islands, except for Javanese itself...

 family (along with other Sumatran languages), whereas Nias appeared to be closest to Central–Eastern Malayo-Polynesian, though these outside connections were only moderately supported (85% confidence). Enggano was not considered, and it is not clear that language is even Austronesian.