install fonts manual in
/usr/local/share/fonts
then create /etc/fonts/conf.avail/65-ubuntu-font-family-arabic.conf
contains
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
<match target="pattern">
<test name="family" compare="eq">
<string>Ubuntu</string>
</test>
<test name="lang" compare="contains">
<string>ar</string>
</test>
<edit name="family" mode="assign" binding="strong">
<string>Ubuntu Arabic</string>
</edit>
</match>
<match target="pattern">
<test name="family" compare="eq">
<string>DejaVu</string>
</test>
<test name="lang" compare="contains">
<string>ar</string>
</test>
<edit name="family" mode="assign" binding="same">
<string>Ubuntu Arabic</string>
</edit>
</match>
<match target="pattern">
<test name="family" compare="eq">
<string>DejaVu Sans</string>
</test>
<test name="lang" compare="contains">
<string>ar</string>
</test>
<edit name="family" mode="assign" binding="same">
<string>Ubuntu Arabic</string>
</edit>
</match>
<match target="pattern">
<test name="family" compare="eq">
<string>DejaVu Serif</string>
</test>
<test name="lang" compare="contains">
<string>ar</string>
</test>
<edit name="family" mode="assign" binding="same">
<string>Ubuntu Arabic</string>
</edit>
</match>
<match target="pattern">
<test name="family" compare="eq">
<string>DejaVu Serif</string>
</test>
<test name="lang" compare="contains">
<string>ar</string>
</test>
<edit name="family" mode="assign" binding="strong">
<string>Ubuntu Arabic</string>
</edit>
</match>
<alias>
<family>DejaVu Serif</family>
<prefer>
<family>Ubuntu Arabic</family>
<family>DejaVu Serif</family>
</prefer>
</alias>
<alias>
<family>DejaVu Sans</family>
<prefer>
<family>Ubuntu Arabic</family>
<family>DejaVu Sans</family>
</prefer>
</alias>
<alias>
<family>DejaVu</family>
<prefer>
<family>Ubuntu Arabic</family>
<family>DejaVu</family>
</prefer>
</alias>
</fontconfig>
and create syslink for it in /etc/fonts/conf.d/