The Tai-Kadai language family is spoken in the People's Republic of China and in Southeast Asia.
The Tai-Kadai language family consists of three branches: 1) Tai, whose most important member is Thai with about 25 million speakers, Southern Thai with 5 million speakers in Thailand, Northern Thai with 5 million speakers in Thailand, Tai Dam in Vietnam and Laos with 3 million speakers and Shan with 3 million speakers in Myanmar. (The spelling Thai is used for the national language of Thailand and very closely related languages for instance Northern Thai and Southern Thai. The spelling Tai is used for the language group and certain languages like Tai D�n or Tai Dam.)
2)Kam-Sui, mainly represented by 2 million persons in the south-east of Guizhou, in the west of Hunan, and in the north of Guangxi, and Sui in Guizhou and Guangxi and other smaller languages, all of them spoken in China.
3) Kadai, consisting of Li spoken on Hainan island, Gelao spoken in the southeast of China and in Vietnam, Ong-Be on Hainan, Laqua in Vietnam and others.
The composition of the Tai-Kadai language family is still matter of dispute: Some theories consider the Tai subgroup genetically related to Sinitic ('Sino-Tai') or to Austronesian ('Austro-Tai').
There are two kinds of script with which the Tai languages are written: 1) Scripts based on Chinese characters used for the central and the northern dialects. 2) Scripts of Indic origin used by the southwestern dialects.
The first written document of a Tai-Kadai language is a Thai Text, which dates back to the year 1293 CE.
The script of modern Thai is of Indic origin. It preserves the ancient distinction between voiced, plain voiceless and aspirated/ejective consonants. This destinction has been abandoned in the modern Thai sound system, but it has left its traces in the distribution of tones. The following languages use scripts similar to the Thai alphabet: Lao, Lü, Tai Dón, Tai Dam. The scripts of Shan and Khamti are also of Indic origin but quite different from the Thai script.
All Tai-Kadai languages are tone languages, i.e. a specific set of lexical tones distinguishes the meaning of words. Tai-Kadai languages have up to nine tones. Thai has five tones, Lao has six tones. In the Kam-Sui subbranch, languages can have up to five tones.
Words in Tai-Kadai languages tend to be monosyllabic and to lack inflectional morphology.
The use of numeral classifiers is very widespread in the Tai-Kadai laguage family. Classifiers are words or affixes which denote the classification of nouns.These words are regularly used with nouns that are counted, in sharp contrast to Indo-European where numerals count nouns directly. Classifiers are also used in languages like Chinese, Korean and Japanese.
The unmarked word order in simple transitive sentences is SVO. Khamti is an exception to that pattern: it has SOV word order.
Due to the strong Chinese influence the Tai-Kadai languages have many Chinese loan words.