Problem

Current default theme's system-ui font-family specifies the following two Chinese fonts:

• "Hiragino Sans GB" (macOS)
• "Microsoft Yahei" (Windows)

These fonts are also installed by default on macOS and Windows with Japanese locales, so Chinese fonts will be displayed even if Japanese is selected as the SiYuan interface language.

Solution 1

Add a Japanese font to the current system-ui font-family:

/* theme.css */
:root {
  --b3-font-family: "Helvetica Neue", "Luxi Sans", "DejaVu Sans", "Hiragino Sans", "Hiragino Sans GB", "Yu Gothic UI", "Microsoft Yahei", sans-serif, "Apple Color Emoji", "Noto Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Android Emoji", "EmojiSymbols";
}

Specifying Japanese fonts as above will degrade the specificity of Chinese fonts and cause new problems in Chinese environments where the Japanese fonts specified here are installed. Also, specifying an internationalized font such as "Segoe UI" did not work either.

Solution 2

Use the :lang() pseudo-class to specify a Japanese font only when Japanese is selected as the interface language:

/* theme.css */
:lang(ja_JP):root {
  --b3-font-family: "Helvetica Neue", "Luxi Sans", "DejaVu Sans", "Hiragino Sans", "Yu Gothic UI", sans-serif, "Apple Color Emoji", "Noto Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Android Emoji", "EmojiSymbols";
}

In this way, appropriate Japanese fonts can be specified without affecting other language environments.

Fixes

Using solution 2, assign "Hiragino Sans" (macOS) and "Yu Gothic UI" (Windows) to system-ui font-family in the current theme.css. This allows the default theme SiYuan, to display appropriate Japanese fonts when Japanese is selected as the interface language.

Thanks for the contribution!
感谢贡献！