CJK is a collective term for Chinese, Japanese, and Korean, which constitute the main East Asian languages. The term is used in the field of software and communications internationalization.
The term CJKV means CJK plus Vietnamese, which in the past used Hán tự/Chinese characters and Chữ Nôm prior to adopting Quốc Ngữ/Latin Alphabet.
These languages all have a shared characteristic: Their writing systems all completely or partly use Chinese characters — hànzì in Chinese, kanji in Japanese, and hanja in Korean. Chinese is written in Chinese characters only and requires c. 4,000 characters for general literacy although there are up to 40,000 characters for reasonably complete coverage. Japanese uses fewer characters — general literacy in Japan can be expected with about 2,000 characters — together with two syllabaries (hiragana and katakana). The use of Chinese characters in Korea is becoming increasingly rare altogether, although idiosyncratic use of Chinese characters in proper names requires knowledge (and therefore availability) of many more characters. The number of characters required for complete coverage of all these languages' needs cannot fit in the 256-character code space of 8-bit character encodings, requiring at least a 16-bit fixed width encoding or multi-byte variable-length encodings. The 16-bit fixed width encodings, such as Unicode up to and including version 2.0, are now deprecated due to the requirement to encode more characters than a 16-bit encoding can accommodate — Unicode 5.0 has some 70,000 Han characters — and the requirement by the Chinese government that software in China support the GB18030 character set.
Although CJK encodings have common character sets, the encodings often used to represent them have been developed separately by different East Asian governments and software companies, and are mutually incompatible. Unicode has attempted, with some controversy, to unify the character sets in a process known as Han unification.
CJK character encodings should consist minimally of Han characters plus language-specific phonetic scripts such as pinyin, bopomofo, hiragana, katakana, and hangul.
CJK character encodings include:
Big5 EUC-JP EUC-KR GB18030 (the mandated standard in the People's Republic of China) GB2312 ISO 2022-JP KS C 5861 Shift-JIS Unicode The CJK character sets take up the bulk of the assigned Unicode code space. There is much controversy among Japanese experts of Chinese characters about the desirability and technical merit of the Han unification process used to map multiple Chinese and Japanese character sets into a single set of unified characters.
All three languages can be written both left-to-right and top-to-bottom, but are usually considered left-to-right scripts when discussing encoding issues.
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