Don't use `--zh-font-family` in languages other than simplified Chinese

[tats-u]

What happened?

Apple system fonts + Latin fonts + sans-serif is sufficient in Traditional Chinese, Korean, and Japanese.
Simplified Chinese fonts (e.g. Microsoft YaHei) are inappropriate, low quality, and ugly in such languages.

(especially) Windows: hiragana & katakana shape are very ugly

Any OSes: shapes of han characters are incorrect.

e.g.

Expect: 🇯🇵骨角曜約記述 🇹🇼骨角曜約記述 🇰🇷骨角曜約記述
Actual: 骨角曜約記述

(code points are the same / uses <span lang="..."> the above to switch languages)

https://heistak.github.io/your-code-displays-japanese-wrong/
https://x.com/Reputeless/status/1929847237745824043?t=zvSXJfOPxZvcRec7vqhdVg

e.g. https://blog.tomoyukim.net/entry/ovsx-vscode-extension/ (one of blogs using this theme; it doesn't modify the default fonts as of 2025-08-20; hiragana & katakana in Microsoft YaHei (Windows) are really ugly and some han shapes are wrong as Japanese kanji)

Hiragana & katakana there are really ugly (in Windows):

We need these hiragana & katakana in Japanese sites instead:

Hugo version

N/A

Theme version

3.29.0

What browsers are you seeing the problem on?

No response

More information about the browser

(especially) Windows but applied to any major OSes / any major browsers

Relevant log output

Link to Minimal Reproducible Example

https://codepen.io/tats-u/pen/jEbzxoz

[tats-u]

The current stack was introduced at 486b5d8, but the past stack, which had been introduced since the initial commit, is also Simplified Chinese dedicated. They are not designed for the other CJK languages at all.