Thanks for your input, @sihosi1812. Sahel seems not to be packaged for Debian yet, right?
At the moment we are following the development of Noto Sans Arabic UI. There have been some upstream fixes to that font which are not yet reflected in Debian/Ubuntu.
Switching to an Arabic locale changes the default font for rendering Arabic script. So one explanation might be that you have specified font settings in your browsers which override the default. But if you seek help to figure it out, Ask Ubuntu is probably a better place.
today I got update that remove language-selector-ar
Ubuntu 20.04
Good. 
Hopefully it installed 56-language-selector-ar.conf too.
no, it didnât
I canât found 56-language-selector-ar.conf on /etc/fonts/conf.d/
I rewrite 69-language-selector-ar.conf and it solve the issue for me
What?? What does this command show for you:
dpkg -L language-selector-common | grep 56
For me it outputs
/etc/fonts/conf.avail/56-language-selector-ar.conf
/etc/fonts/conf.d/56-language-selector-ar.conf
i.e. the new .conf file and a symlink to it.
I found it on avail only
dpkg -L language-selector-common | grep 56
/etc/fonts/conf.avail/56-language-selector-ar.conf
Weird. Then can you please run this command:
sudo apt install --reinstall language-selector-common
and let us know if that adds the symlink. If it does, then please remove 69-language-selector-ar.conf and tell us if it still works.
No changes, I removed â69-language-selector-en.confâ and re-applied the steps and it didnât fix the problem
This is indeed a mystery. Can you show the complete terminal output from the command:
sudo apt install --reinstall language-selector-commonI got
Reinstallation of language-selector-common is not possible, it cannot be downloaded.
[xlmnxp@lucid ~]$ sudo apt install --reinstall language-selector-common
[sudo] password for xlmnxp:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reinstallation of language-selector-common is not possible, it cannot be downloaded.
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
I suspect a problem with the archive mirror you are using. Would suggest that you open Software & Updates and change the Download from: setting to âMain serverâ. Then:
sudo apt update
sudo apt install --reinstall language-selector-commonthe mirror is up to date
I will try main server
same thing in main server
[xlmnxp@lucid ~]$ sudo apt update
Hit:1 http://archive.canonical.com/ubuntu focal InRelease
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease
Hit:3 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:4 https://packages.microsoft.com/ubuntu/20.04/prod focal InRelease
Hit:5 https://packages.microsoft.com/repos/ms-teams stable InRelease
Hit:6 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:7 http://archive.ubuntu.com/ubuntu focal-security InRelease
Hit:8 https://download.mono-project.com/repo/ubuntu vs-bionic InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
1 package can be upgraded. Run 'apt list --upgradable' to see it.
[xlmnxp@lucid ~]$ sudo apt install --reinstall language-selector-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reinstallation of language-selector-common is not possible, it cannot be downloaded.
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
What does this output:
dpkg -l language-selector-commonBtw, another thing you may want to try:
sudo apt install language-selector-common=0.204.2 language-selector-gnome=0.204.2[xlmnxp@lucid ~]$ dpkg -l language-selector-common
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-========================-============-============-=================================
ii language-selector-common 0.304 all Language selector for Ubuntu
that command downgrading language-selector-common and language-selector-gnome from 0.304 to 0.204.2 but it fix the issue 
Ok, good. Only you can tell how you succeeded in installing 0.304. 
How it installed xD
maybe when I add PPA for UKUI DE or maybe something else