Telex (IME)

Telex, also known in Vietnamese as Quốc ngữ điện tín (lit. "national language telex", is a convention for encoding Vietnamese text in plain ASCII characters. Originally used for transmitting Vietnamese text over telex systems, it is now a popular input method for computers.

The Telex input method is based on a set of rules for transmitting accented Vietnamese text over telex (máy điện tín) first used in Vietnam during the 1920s and 1930s. Telex services at the time ran over infrastructure that was designed overseas to handle only a basic Latin alphabet, so a message reading "vỡ đê" ("the dam broke") could easily be misinterpreted as "vợ đẻ" ("the wife is giving birth"). Nguyễn Văn Vĩnh, a prominent journalist and translator, is credited with devising the original set of rules for telex systems.

In later decades, common computer systems came with largely the same limitations as the telex infrastructure, namely inadequate support for the large number of characters in Vietnamese. Mnemonics like Telex and Vietnamese Quoted-Readable (VIQR) were adapted for these systems. As a variable-width character encoding, Telex represents a single Vietnamese character as one, two, or three ASCII characters. By contrast, a byte-oriented code page like VISCII takes up only one byte per Vietnamese character but requires specialized software or hardware for input.

In the 1980s and 1990s, Telex was adopted as a way to type Vietnamese on standard English keyboards. Specialized software converted Telex keystrokes to either precomposed or decomposed Unicode text as the user typed. VietStar was the first such software package to support this entry mode. The Bked editor by Quách Tuấn Ngọc extended Telex with commands such as z, [ for "ư", and ] for "ơ". It was further popularized with the input method editors VietKey, Vietres, and VPSKeys. In 1993, the use of Telex as an input method was standardized in Vietnam as part of TCVN 5712.

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