~/.config/fontconfig/fonts.conf

fonts.conf

<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
    <match target="pattern">
        <test name="family" qual="any">
            <string>monospace</string>
        </test>
        <edit name="family" mode="assign" binding="same">
            <string>Fira Mono</string>
            <string>Source Han Sans HW TC</string>
        </edit>
    </match>
    <match target="pattern">
        <test name="family" qual="any">
            <string>sans-serif</string>
        </test>
        <edit name="family" mode="assign" binding="strong">
            <string>Fira Sans</string>
            <string>Source Han Sans TC</string>
            <string>Noto Emoji</string>
            <string>unifont</string>
        </edit>
    </match>
    <match target="pattern">
        <test name="family" qual="any">
            <string>serif</string>
        </test>
        <edit name="family" mode="assign" binding="strong">
            <string>Fira Sans</string>
            <string>Source Han Sans TC</string>
            <string>Noto Emoji</string>
            <string>unifont</string>
        </edit>
    </match>
    <match target="pattern">
        <test name="family" qual="any">
            <string>serif</string>
        </test>
        <edit name="family" mode="assign" binding="same">
            <string>AR PL UMing TW</string>
        </edit>
    </match>
    <alias>
            <family>monospace</family>
        <prefer>
            <family>Fira Mono</family>
            <family>Noto Sans Mono CJK TC</family>
        </prefer>
    </alias>
    <alias>
            <family>sans-serif</family>
        <prefer>
            <family>Fira Sans</family>
            <family>Noto Emoji</family>
        </prefer>
    </alias>
    <alias>
            <family>serif</family>
        <prefer>
            <family>Fira Sans</family>
            <family>Noto Emoji</family>
        </prefer>
    </alias>
    <alias>
            <family>serif</family>
        <prefer>
            <family>AR PL UMing TW</family>
        </prefer>
    </alias>
    <match target="pattern">
        <test name="family" qual="any">
            <string>Roboto</string>
        </test>
        <edit name="family" mode="assign" binding="same">
            <string>Source Han Sans TC</string>
        </edit>
    </match>
    <match target="pattern">
        <test name="family" qual="any">
            <string>Arial</string>
        </test>
        <edit name="family" mode="assign" binding="same">
            <string>Source Han Sans TC</string>
        </edit>
    </match>
</fontconfig>