[Fontconfig] Fix TW-Kai Pollution

Problem Link to heading

TW-Kai pollutes the monospace font in the gnome terminal.

For the sake of displaying most of the CJK characters in Linux, you might get the solution of installing TW-Kai and TW-Sung fonts after googling. However, some applications may look strange after installing them.

Solution Link to heading

If the font cannot display the character, it will ask other fonts for help. And there is an order to ask for help. Unfortunately, the priority of TW-Kai and TW-Sung is higher than the other CJK fonts in some Linux distributions. Therefore, we can fix the problem by setting the default fonts and adjusting the fallback order.

Edit ~/.config/fontconfig/fonts.conf like below:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">

<fontconfig>

    <!-- Default serif fonts -->
    <match>
        <test name="family">
            <string>serif</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>Noto Serif</string>
            <string>Noto Serif CJK TC</string>
            <string>Noto Serif CJK SC</string>
            <string>Noto Serif CJK JP</string>
            <string>Noto Serif CJK KR</string>
        </edit>
    </match>

    <!-- Default sans-serif font -->
    <match>
        <test name="family">
            <string>sans-serif</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>Noto Sans</string>
            <string>Noto Sans CJK TC</string>
            <string>Noto Sans CJK SC</string>
            <string>Noto Sans CJK JP</string>
            <string>Noto Sans CJK KR</string>
        </edit>
    </match>

    <!-- Default monospace fonts -->
    <match>
        <test name="family">
            <string>monospace</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>Inconsolata</string>
            <string>Noto Sans Mono CJK TC</string>
            <string>Noto Sans Mono CJK SC</string>
            <string>Noto Sans Mono CJK JP</string>
            <string>Noto Sans Mono CJK KR</string>
        </edit>
    </match>

    <!-- Fallback fonts preference order -->
    <alias>
        <family>serif</family>
        <prefer>
            <family>Noto Serif</family>
            <family>Noto Serif CJK TC</family>
            <family>Noto Serif CJK SC</family>
            <family>Noto Serif CJK JP</family>
            <family>Noto Serif CJK KR</family>
            <family>Noto Color Emoji</family>
            <family>Noto Emoji</family>
        </prefer>
        <default>
            <family>TW-Sung</family>
            <family>TW-Sung-Plus</family>
            <family>TW-Sung-Ext-B</family>
            <family>TW-Kai</family>
            <family>TW-Kai-Plus</family>
            <family>TW-Kai-Ext-B</family>
        </default>
    </alias>
    <alias>
        <family>sans-serif</family>
        <prefer>
            <family>Noto Sans</family>
            <family>Noto Sans CJK TC</family>
            <family>Noto Sans CJK SC</family>
            <family>Noto Sans CJK JP</family>
            <family>Noto Sans CJK KR</family>
            <family>Noto Color Emoji</family>
            <family>Noto Emoji</family>
        </prefer>
        <default>
            <family>TW-Sung</family>
            <family>TW-Sung-Plus</family>
            <family>TW-Sung-Ext-B</family>
            <family>TW-Kai</family>
            <family>TW-Kai-Plus</family>
            <family>TW-Kai-Ext-B</family>
        </default>
    </alias>
    <alias>
        <family>monospace</family>
        <prefer>
            <family>Inconsolata</family>
            <family>Noto Sans Mono</family>
            <family>Noto Sans Mono CJK TC</family>
            <family>Noto Sans Mono CJK SC</family>
            <family>Noto Sans Mono CJK JP</family>
            <family>Noto Sans Mono CJK KR</family>
            <family>Noto Color Emoji</family>
            <family>Noto Emoji</family>
        </prefer>
        <default>
            <family>TW-Sung</family>
            <family>TW-Sung-Plus</family>
            <family>TW-Sung-Ext-B</family>
            <family>TW-Kai</family>
            <family>TW-Kai-Plus</family>
            <family>TW-Kai-Ext-B</family>
        </default>
    </alias>

</fontconfig>

After editing the fonts.conf, you need to run $ fc-cache -f to rebuild the font cache.

You can check the order by $ fc-match -s serif, $ fc-match -s sans-serif, and $ fc-match -s monospace.

Note

<alias> is the shortcut to adjust the priority of the fallback fonts.

In the end, the order will be like this: <prefer> -> original -> <accept> -> <default>

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