sudo gedit /etc/fonts/conf.avail/69-language-selector-ar.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <!-- Arabic (ar) -->
    <match target="pattern">
        <test name="lang" compare="contains">
            <string>ar</string>
        </test>
        <test qual="any" name="family">
            <string>serif</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>KacstOne</string>
        </edit>
    </match>


    <match target="pattern">
        <test name="lang" compare="contains">
            <string>ar</string>
        </test>
        <test qual="any" name="family">
            <string>sans-serif</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>KacstOne</string>
        </edit>
    </match>


    <match target="pattern">
        <test name="lang" compare="contains">
            <string>ar</string>
        </test>
        <test qual="any" name="family">
            <string>monospace</string>
        </test>
        <edit name="family" mode="prepend" binding="strong">
            <string>Thabit</string>
          
        </edit>
    </match>
    <!-- Arabic (ar) ends -->
</fontconfig>

cd /etc/fonts/conf.d && sudo ln -s ../conf.avail/69-language-selector-ar.conf .