Khmer, or Cambodian, is the language of the Khmer people and the official language of Cambodia. One of the more prominent Austroasiatic languages, the language has been considerably influenced by Sanskrit and Pali, especially in the royal and religious registers, through the vehicles of Hinduism and Buddhism. As a result of geographic proximity, the Khmer language has affected, and also been affected by, Thai, Lao, Vietnamese and Cham which all form a sprachbund in peninsular Southeast Asia. Khmer differs from neighboring languages such as Thai, Lao and Vietnamese in that it is not a tonal language. It has three main dialects that are mutually intelligible: * Battambang (considered the standard) * Phnom Penh * Northern Khmer, also known as Khmer Surin, spoken by ethnic Khmer native to Northeast Thailand * Cardamom Khmer, an archaic form spoken by a small population in the Cardamom Mountains of western Cambodia. History Linguistic study of the Khmer language divides its history into four periods. Pre-Angkorian Khmer, the language after its divergence from Proto-Mon-Khmer until the ninth century, is only known from words and phrases in Sanskrit texts of the era. Old Khmer (or Angkorian Khmer) is the language as it was spoken in the Khmer Empire from the 9th century until the weakening of the empire sometime in the 13th century. Old Khmer is attested by many primary sources and has been studied in depth by a few scholars, most notably Saveros Pou, Phillip Jenner and Heinz-Jürgen Pinnow. Following the end of the Khmer Empire the language lost the standardizing influence of being the language of government and accordingly underwent a turbulent period of change in morphology, phonology and lexicon. The language of this transition period, from about the 14th to 18th centuries, is referred to as Middle Khmer and saw borrowing from Thai, Lao and, to a lesser extent, Vietnamese. The changes during this period are so profound that the rules of Modern Khmer can not be applied to correctly understand the Old Khmer. The language became recognizable as the Modern Khmer spoken today in the 19th century. Khmer is classified as a member of the Eastern branch of the Mon-Khmer language family, itself a subdivision of the larger Austro-Asiatic language group, which has representatives in a large swath of land from Northeast India down through Southeast Asia to the Malay Peninsula and its islands. As such, its closest relatives are the languages of the Pearic, Bahnaric, and Katuic families spoken by the hill tribes of the region. The Vietic languages have also been classified as belonging to this family.

Thai is the national and official language of Thailand and the mother tongue of the Thai people, Thailand's dominant ethnic group. Thai is a member of the Tai group of the Tai-Kadai language family. The Tai-Kadai languages are thought to have originated in what is now southern China, and some linguists have proposed links to the Austroasiatic, Austronesian, or Sino-Tibetan language families. It is a tonal and analytic language. The combination of tonality, a complex orthography, relational markers and a distinctive phonology can make Thai difficult to learn for those who do not already speak a related language. Standard Thai, also known as Central Thai or Siamese, is the official language of Thailand, spoken by about 65 million people including speakers of Bangkok Thai . Khorat Thai is spoken by about 400,000 (1984) in Nakhon Ratchasima; it occupies a linguistic position somewhere between Central Thai and Isan on a dialect continuum, and may be considered a variant or dialect of either. In addition to Standard Thai, Thailand is home to other related Tai languages, including: * Isan (Northeastern Thai), the language of the Isan region of Thailand, considered by some to be a dialect of the Lao language, which it very closely resembles (although it is written in the Thai alphabet). It is spoken by about 15 million people (1983). * Nyaw language, spoken mostly in Nakhon Phanom Province, Sakhon Nakhon Province, Udon Thani Province of Northeast Thailand. * Galung language, spoken in Nakhon Phanom Province of Northeast Thailand. * Lü (Tai Lue, Dai), spoken by about 78,000 (1993) in northern Thailand. * Northern Thai (Lanna, Kam Meuang, or Thai Yuan), spoken by about 6 million (1983) in the formerly independent kingdom of Lanna (Chiang Mai). * Phuan, spoken by an unknown number of people in central Thailand and Isan. * Phu Thai, spoken by about 156,000 around Nakhon Phanom Province (1993). * Shan (Thai Luang, Tai Long, Thai Yai), spoken by about 56,000 in north-west Thailand along the border with the Shan States of Burma (1993). * Song, spoken by about 20,000 to 30,000 in central and northern Thailand (1982). * Southern Thai (Pak Dtai), spoken about 5 million (1990). * Thai Dam, spoken by about 20,000 (1991) in Isan and Saraburi Province. Many of these languages are spoken by larger numbers outside of Thailand. Most speakers of dialects and minority languages speak Central Thai as well, since it is the language used in schools and universities all across the kingdom. Numerous languages not related to Thai are spoken within Thailand by ethnic minority hill tribespeople. These languages include Hmong-Mien (Yao), Karen, Lisu, and others. Standard Thai is composed of several distinct registers, forms for different social contexts: * Street Thai : informal, without polite terms of address, as used between close relatives and friends. * Elegant Thai : official and written version, includes respectful terms of address; used in simplified form in newspapers. * Rhetorical Thai: used for public speaking. * Religious Thai: (heavily influenced by Sanskrit and P?li) used when discussing Buddhism or addressing monks. * Royal Thai : (influenced by Khmer) used when addressing members of the royal family or describing their activities. Many Thais can speak at only the first and second levels, though they will understand the others.