Thailand , China, Laos and Vietnam.

Thai (sometimes referred to as Siamese), is one of the oldest languages in East and South-East Asia and is part of the Tai language family. All members of the Tai family derive from a single proto-parent designated asProto-Tai. Linguistic research has pointed to the area near the border of northern Vietnam and southeastern China as the probable place of origin for the Tai languages.

Through the centuries, Mon, Khmer, Sanskrit, and Pali have all influenced the Thai language in both vocabulary and grammatical structures. More recently, Chinese and English words relating to business, commerce, and cuisine have been integrated into the language.

The classification of dialects is further complicated by the fact that Lao, the language spoken in Laos, is also called Eastern Thai; Lanna, spoken in the Thailand's northern provinces, is also called Northern Thai; and Isan, which is spoken in northeastern Thailand, is also called Northeastern Thai. Not all of these dialects are mutually comprehensible.

The origin of the Thai alphabet is the subject of much debate amongst linguists, but it is likely that its roots spring from the Brahmi script of South India. It is also believed that the Thai alphabet was derived from, or at least influenced by, the Old Khmer alphabet. According to tradition it was created in 1283 by King Ramkhamhaeng (1275-1317).

This is a syllabic alphabet consisting of 44 basic consonants, each with an inherent vowel. The 18 other vowels and 6 diphthongs are indicated using diacritics which appear in front of, above, below or after the consonants they modify. 8 of the letters are used only for writing words of Pali and Sanskrit origin.

The words are written from left to right and there are no spaces between words, instead spaces in a Thai text indicate the end of a clause or sentence.

• Thai is a tonal language, which means that the same word can convey different meanings depending on the tone applied when the particular word is pronounced. There are five tones: low, high, mid-pitch, rising, and falling. Four of these tones are indicated by signs over the consonants, while the fifth is indicated by the absence of a sign. As a tonal language, Thai is devoid of inflection (such as the rising voice an English speaker might use to show that he is asking a question). Instead, mood, questions, negation, and other parts of speech are constructed by adding certain words to sentences.
• Some aspects of Thai grammar are far simpler than in other languages. For example, there are no gendered or numbered nouns in Thai, and there are no cases. There are also no verb conjugations in Thai. The same verb form is used regardless of the subject of the sentence. Thai verbs also do not change form in different tenses, such as present, past, or future. Instead, distinctions between tenses are marked by adverbs and expressions of time or by the context of the sentence.
• Most Thai words are monosyllabic. More complex words generally may be formed by combining two monosyllabic words. There are, however, some polysyllabic words, especially those borrowed from Sanskrit, English, and other languages that cannot be broken down into monosyllabic components.