Question: What are the main dialects of Thai?

Languages of Thailand


An ethnolinguistic map of Thailand. Thailand, and its neighbor Laos, are dominated by languages of the Southwestern Tai family. Karen languages are spoken along the border with Burma, Khmer is spoken near Cambodia and Malay in the south near Malaysia. The following table comprises all 62 ethnic groups recognised by the Royal Thai Government in the 2011 Country Report to the UN Committee responsible for the International Convention for the Elimination of All Forms of Racial Discrimination, available from the Department of Rights and Liberties Promotion of the Thai Ministry of Justice.[1]:3

The following table shows all the language families of Northeast Thailand, as recognised in the same report.

Note that population numbers are for the Northeast region only. Languages may have additional speakers outside the Northeast.
The Thai hill tribes speak numerous small languages, many Chinese retain varieties of Chinese, and there are half a dozen sign languages. The  reports 73 living languages are used in Thailand. The Royal Thai Government's 2011 Country Report to the Committee Responsible for the International Convention on the Elimination of All Forms of Racial Discrimination,[1] relying mainly on the 2005 Ethnolinguistic Maps of Thailand data,[2] lists 62 languages.
Thais
In Thailand the four major dialects of Thai are: Central Thai, Thai version of Lao which is called Isan, Southern Thai and Northern Thai language.
The sole official language of Thailand is Central Thai, a Kra-Dai language closely related to Lao, Shan in Burma, and numerous smaller languages of southern China and northern Vietnam. It is the principal language of education and government and is spoken throughout the country. The standard is written in the Thai alphabet, an abugida that evolved from the Khmer script. However, Central Thais speak an folk language in Central (including the metropolitan area), Eastern, Southwestern Thailand and Nakhon Ratchasima Province.
Several other Tai languages exist: Southern Thai is spoken in the provinces that were formerly part of the vassal state of Nakhon Si Thammarat, and Northern Thai is spoken in the provinces that were formerly part of the independent kingdom of Lanna.
Minority languages
In the far south, Yawi, a dialect of Malay, is the primary language of the Malay Muslims. Khmer are spoken by the elder Northern Khmer. Varieties of Chinese are also spoken by the elder Thai Chinese population, with the Teochew dialect being best represented. However, the younger Northern Khmer trend to speak Central Thai, younger Thai Chinese speak Central Thai, and Peranakan speak Southern Thai language only.
Tribal languages
Numerous tribal languages are also spoken, including those belonging to:
The Mon–Khmer family, such as Mon, Khmer, Mlabri, Lawa and Orang Asli.
The Austronesian family, such as Urak Lawoi' and Moken.
The Sino-Tibetan family such as Akhan, and Karen.
Other Tai languages such as Nyaw, Phu Thai, Yoy and Saek.
Hmong is a member of the Hmong–Mien languages, which is now regarded as a language family of its own.
Sign language
Several village sign languages are reported among the hill tribes, though it is not clear whether these are independent languages, as only Ban Khor Sign Language has been described. Two related deaf-community sign languages developed in Chiangmai and Bangkok; the national Thai Sign Language developed from these under the influence of American Sign Language.
English is a mandatory school subject, but the number of fluent speakers remains very low, especially outside the cities.
Most widely spoken language
The following table shows official first languages in Thailand with equal to or more than 400,000 speakers according to the Royal Thai Government's 2011 Country Report to the Committee Responsible for the International Convention on the Elimination of All Forms of Racial Discrimination,[1] mainly using the Ethnolinguistic Maps of Thailand data.[2]
Official first languages of Thailand with equal to or more than 400,000 speakers[1]

Languages in Thailand with more than 1 million speakers according to Ethnologue

The following table employs 2000 census data. Caution should be exercised with Thai census data on first language. In Thai censuses, the four largest Tai-Kadai languages of Thailand (in order, Central Thai, Isan (majority Lao),[3] Kam Mueang, Pak Tai) are not provided as options for language or ethnic group. People stating such a language as a first language, including Lao, are allocated to 'Thai'.[4] This explains the disparity between the two tables. For instance, self-reporting as Lao has been prohibited, due to the prohibition of the Lao ethnonym in the context of describing Thai citizens, for approximately one hundred years.[5][6] This was due to the promotion of a 'Thai' national identity to cement Siamese claims over the Lao city-states of what is now Northern and Northeast Thailand following the 1893 Franco Siamese War and subsequent threat posed by French Indochina to Lao tributary states of Siam. Some historian argued that the birth of a homogenizing Thai ethnocentric national identity sufficient to begin transforming Siam from an absolute monarchy into a modern nation-state was achieved by assimilating the Lao within this Thai 'identity', equivalent to what is now known as the Tai–Kadai_languages, under a 'Greater Thai Empire', and can be traced back to at least 1902. But this view neglects the fact that "Lao", as a unified ethnic group, was also created by the French in order to sever the Siamese influence over Lan Xang and to justify the annexation of "Laos" -- as a created territory -- to its Indochinese "protectorate." [7] The 2011 Country Report data is therefore more comprehensive and better differentiates between the large Tai-Kadai languages of Thailand. As a country submission to a UN convention ratified by Thailand, it is also arguably more authoritative. 

Provincial language data

See also
Demographics of Thailand
Further reading
L-Thongkum, Theraphan. 1985. Minority Languages of Thailand. In Science of Language Papers: Languages and Dialects. vol 5. Department of Linguistics, Faculty of Arts, Chulalongkorn University.
Suwilai Premsrirat. 2004. "Using GIS For Displaying An Ethnolinguistic Map of Thailand." In Papers from the Eleventh Annual Meeting of the Southeast Asian Linguistics Society, edited by Somsonge Burusphat. Tempe, Arizona, 599-617. Arizona State University, Program for Southeast Asian Studies.

ไทย

Languages of Thailand at Muturzikin.com
[1] at Ethnologue