Mon-Khmer language, the native language of 60–65 million people in Vietnam and a second language for many members of Vietnam's more than 50 minority ethnic groups, with some 2 million speakers outside the country. For much of Vietnam's history, Classical Chinese was the dominant literary language, and Chinese vocabulary given a Vietnamese pronunciation (“Sino-Vietnamese”) remains a significant part of the language's lexicon. By the 13th century Chinese characters were adapted to write native Vietnamese words. In the 17th century Roman Catholic missionaries introduced a system of writing Vietnamese in the Latin alphabet with diacritics distinguishing vowel qualities and tones, a system that was widely adopted only in the 20th century.

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