How to change the default font using font-config
If you want to replace the default font used for a certain family such as sans-serif or monospace or just want to replace every occurrence of a font, you need to deal with font-config. This is very simple.
First you need to create a file with name fonts.conf
in ~/.config/fontconfig
folder. If that file exists, You have to add contents between <fontconfig>..</fontconfig>
Tag.
To replace Ubuntu font with Aller, Your font config should have the lines between the <fontconfig>
tags.
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
<match target="pattern" name="family">
<test name="family" qual="any">
<string>Ubuntu</string>
</test>
<edit name="family" mode="assign" binding="strong">
<string>Aller</string>
</edit>
</match>
</fontconfig>
For a detailed information, Have a look a font-config manual page.