Presently, the written language uses the Vietnamese alphabet (quốc ngữ or "national script", literally "national language"), based on the Latin alphabet. Originally a Romanization of Vietnamese, it was codified in the 17th century by a French Jesuit missionary named Alexandre de Rhodes (1591–1660), based on works of earlier Portuguese missionaries (Gaspar de Amaral and António de Barbosa). The use of the script was gradually extended from its initial domain in Christian writing to become more popular among the general public.
Under French colonial rule, the script became official and required for all public documents in 1910 by issue of a decree by the French Résident Supérieur of the protectorate of Tonkin. By the end of first half 20th century virtually all writings were done in quốc ngữ.
Changes in the script were made by French scholars and administrators and by conferences held after independence during 1954–1974. The script now reflects a so-called Middle Vietnamese dialect that has vowels and final consonants most similar to northern dialects and initial consonants most similar to southern dialects (Nguyễn 1996). This Middle Vietnamese is presumably close to the Hanoi variety as spoken sometime after 1600 but before the present.Free Quote
Before French rule, the first two Vietnamese writing systems were based on Chinese script:
the standard Chinese character set called chữ nho (scholar's characters, 字儒): used to write Literary Chinese
a complicated variant form known as chữ nôm (southern/vernacular characters, 字喃) with characters not found in the Chinese character set; this system was better adapted to the unique phonetic aspects of Vietnamese which differed from Chinese
The authentic Chinese writing, chữ nho, was in more common usage, whereas chữ nôm was used by members of the educated elite (one needs to be able to read chữ nho in order to read chữ nôm). Both scripts have fallen out of common usage in modern Vietnam, and chữ nôm is nearly extinct.