Background reading:
There are four main differences between Latin and CJK fonts that are important to consider when typesetting:
1. Full-width, monospaced
Latin fonts are mostly proportional by default, but most CJK fonts are monospaced. Chinese and Japanese fonts are designed to fit the full em square. Some Japanese fonts have smaller widths for narrower typesetting, but the default for Japanese fonts is monospaced. Korean fonts are little more complicated—Hangeul, the Korean script, is monospaced by default, but the punctuation is proportional because Korean fonts use Latin punctuation—and also a wordspacing system (see point 3). While Chinese and Japanese monospaced fonts are usually full-width, a recent trend in Korea is to make the letter width narrow, around 850–950 units, for smoother readability and a more modern feel.
2. Use of punctuation
CJK scripts have a special punctuation in common called “full-width punctuation.” This is used in all CJK fonts, but the usage differs among them. In Japanese, full-width punctuation is used by default, with Latin punctuation used only in special and formal cases, such as dissertation papers.
In Chinese, both Latin and full-width punctuation are used, but with Traditional Chinese usage in Hong Kong and Taiwan, commas are placed in the middle of the letter height. Latin punctuation and full-width punctuation are all used for a different meaning and purpose.
In Korean, the default punctuation is Latin, and there's no full-width punctuation. For brackets, full-width punctuation is allowed, but only in limited special scenarios. For example, when noting bibliographic references, both 「」and『』are used. However, commas and periods are strictly Latin, shape-wise, and full-width punctuation is never used in that position. And for the wordspaces and Latin punctuation, most Korean fonts have a Korean version of those characters, with a better size and baseline, because regular Latin punctuation does not usually align well with Hangeul.
3. Balance: the center of gravity, not the baseline
CJK fonts do not have a concept of a baseline. The idea is that the balance of the type exists roughly in the center of the em square (remembering that that box is not necessarily a square if the font is proportional), and therefore the right center of gravity depends on the design of the typeface and the writing direction. Usually the balance is set at the middle, but it can shift up or down. Usually when the center of gravity is high, the font is likely to look more sophisticated and elegant; when it’s low, more casual.
4. No italics
In CJK scripts—and therefore CJK fonts—there are no italics. Type is sometimes faux-italicized for design purposes, but true italics do not exist. Instead, designers come up with creative solutions. Most of the time, single and double quotation marks or full-width brackets are the common and easy way to indicate emphasis. Little dots above the letters are also used a lot when there is no Ruby (small text written above Kanji or foreign letters to indicate phonetics or pronunciations in Japanese). In Japanese, use of Katakana is sometimes used for emphasis.
Underlines are also used, but more for subtitles than emphasis in the middle of a paragraph. If the design allows, wavy or highlighted underlines are also used. Bolding and coloring of words are good solutions, too.
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