The Mainland Southeast Asia linguistic area is a sprachbund including languages of the Sino-Tibetan, Hmong–Mien (or Miao–Yao), Kra–Dai, Austronesian and Austroasiatic families spoken in an area stretching from Thailand to China. Neighbouring languages across these families, though presumed unrelated, often have similar typological features, which are believed to have spread by diffusion. James Matisoff referred to this area as the "Sinosphere", contrasted with the "Indosphere", but viewed it as a zone of mutual influence in the ancient period.
Language distribution
The Austroasiatic languages include Vietnamese and Khmer, as well as many other languages spoken in scattered pockets as far afield as Malaya and eastern India. Most linguists believe that Austroasiatic languages once ranged continuously across southeast Asia and that their scattered distribution today is the result of the subsequent migration of speakers of other language groups from southern China.
Chinese civilization and the Chinese language spread from their home in the North China Plain into the Yangtze valley and then into southern China during the first millennium BC and first millennium AD. Indigenous groups in these areas either became Chinese, retreated to the hill country, or migrated to the south. Thus the Kra–Dai languages, today including Thai, Lao and Shan, were originally spoken in what is now southern China, where the greatest diversity within the family is still found, and possibly as far north as the Yangtze valley. With the exception of Zhuang, most of the Kra–Dai languages still remaining in China are spoken in isolated upland areas. Similarly the Hmong–Mien languages may originally have been spoken in the middle Yangtze. Today they are scattered across isolated hill regions of southern China. Many of them migrated to southeast Asia in the 18th and 19th centuries, after the suppression of a series of revolts in Guizhou.
The upland regions of the interior of the area, as well as the plains of Burma, are home to speakers of other Sino-Tibetan languages, the Tibeto-Burman languages. The Austronesian languages, spoken across the Pacific and Indian Oceans, are represented in MSEA by the divergent Chamic group.
The far southern Sinitic languages Cantonese and Pinghua are also part of the Mainland Southeast Asia linguistic area, as demonstrated by Hilário de Sousa (2015).
Mark Post (2015) observes that the Tani languages of Arunachal Pradesh, Northeast India typologically fit into the Mainland Southeast Asia linguistic area, which typically has creoloid morphosyntactic patterns, rather than with the languages of the Tibetosphere. Post (2015) also notes that Tani culture is similar to those of Mainland Southeast Asian hill tribe cultures, and is not particularly adapted to cold montane environments.
David Gil (2015) considers the Mainland Southeast Asia linguistic area to be part of the larger Mekong-Mamberamo linguistic area, which also includes languages in Indonesia west of the Mamberamo River.
Syllable structure
A characteristic of MSEA languages is a particular syllable structure involving monosyllabic morphemes, lexical tone, a fairly large inventory of consonants, including phonemic aspiration, limited clusters at the beginning of a syllable, and plentiful vowel contrasts. Final consonants are typically highly restricted, often limited to glides and nasals or unreleased stops at the same points of articulation, with no clusters and no voice distinction. Languages in the northern part of the area generally have fewer vowel and final contrasts but more initial contrasts.
Most MSEA languages tend to have monosyllabic morphemes, but there are exceptions. Some polysyllabic morphemes exist even in Old Chinese and Vietnamese, often loanwords from other languages. A related syllable structure found in some languages, such as the Mon–Khmer languages, is the sesquisyllable (from meaning "one and a half"), consisting of a stressed syllable with approximately the above structure, preceded by an unstressed "minor" syllable consisting only of a consonant and a neutral vowel . That structure is present in many conservative Mon–Khmer languages such as Khmer (Cambodian), as well as in Burmese, and it is reconstructed for the older stages of a number of Sino-Tibetan languages.
Tone systems
Phonemic tone is one of the most well-known of southeast Asian language characteristics. Many of the languages in the area have strikingly similar tone systems, which appear to have developed in the same way.