nixos-config/home-manager/profiles/fontconfig/fonts.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
<!-- https://catcat.cc/post/2021-03-07/ -->
<fontconfig>

  <match target="pattern">
    <test name="family">
      <string>system-ui</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>sans-serif</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="family">
      <string>sans-serif</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans</string>
      <string>Noto Sans CJK SC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="family">
      <string>serif</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif</string>
      <string>Noto Serif CJK SC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="family">
      <string>monospace</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>RobotoMono Nerd Font Mono</string>
      <string>Noto Sans Mono CJK SC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="family">
      <string>emoji</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Color Emoji</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>ja</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Sans CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans CJK JP</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>ja</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Serif CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif CJK JP</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>ko</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Sans CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans CJK KR</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>ko</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Serif CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif CJK KR</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-CN</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Sans</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans CJK SC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-CN</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Serif</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif CJK SC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-HK</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Sans CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans CJK HK</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-HK</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Serif CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif CJK HK</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-TW</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Sans CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Sans CJK TC</string>
    </edit>
  </match>

  <match target="pattern">
    <test name="lang" compare="contains">
      <string>zh-TW</string>
    </test>
    <test name="family" compare="contains">
      <string>Noto Serif CJK SC</string>
    </test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Serif CJK TC</string>
    </edit>
  </match>

</fontconfig>