Hi,
please let me understand the flow.
You started the live O.S. from the latest livecd or livedvd ISO? Then you run the calamares installer, selected Arabic language and installed. Then the system was in Arabic since first boot into the installed system? Next you updated the system and lost the Arabic language?
There are no relevant updates in the last days which might cause the problem of removing a configured language, unless what you report is instead a problem with Plasma desktop, which has been updated very recently.
What is the output of:

grep -v "^#" /etc/locale.gen
cat /etc/locale.conf

System locale is configured in /etc/locale.gen and compiled with sudo locale-gen and this should have been done at installion time.

This said, what exactly happened here is not clear, maybe I can reproduce it by repeating your installation flow but I first try to retrieve some more information as described above because the option of trying to reproduce it myself requires more time.

Thanks for quick reply

Yes you're right the system in first boot after install was in Arabic but after update with (sudo dnf update) and reboot it turned to English. I started OS from LiveDVD Plasma ISO

output of grep -v "^#" /etc/locale.gen is:

ar_AE.UTF-8 UTF-8
ar_BH.UTF-8 UTF-8
ar_DZ.UTF-8 UTF-8
ar_EG.UTF-8 UTF-8
ar_IN UTF-8
ar_IQ.UTF-8 UTF-8
ar_JO.UTF-8 UTF-8
ar_KW.UTF-8 UTF-8
ar_LB.UTF-8 UTF-8
ar_LY.UTF-8 UTF-8
ar_MA.UTF-8 UTF-8
ar_OM.UTF-8 UTF-8
ar_QA.UTF-8 UTF-8
ar_SA.UTF-8 UTF-8
ar_SD.UTF-8 UTF-8
ar_SS UTF-8
ar_SY.UTF-8 UTF-8
ar_TN.UTF-8 UTF-8
ar_YE.UTF-8 UTF-8
en_AG UTF-8
en_AU.UTF-8 UTF-8
en_BW.UTF-8 UTF-8
en_CA.UTF-8 UTF-8
en_DK.UTF-8 UTF-8
en_GB.UTF-8 UTF-8
en_HK.UTF-8 UTF-8
en_IE.UTF-8 UTF-8
en_IL UTF-8
en_IN UTF-8
en_NG UTF-8
en_NZ.UTF-8 UTF-8
en_PH.UTF-8 UTF-8
en_SC.UTF-8 UTF-8
en_SE.UTF-8 UTF-8
en_SG.UTF-8 UTF-8
en_US.UTF-8 UTF-8
en_ZA.UTF-8 UTF-8
en_ZM UTF-8
en_ZW.UTF-8 UTF-8

ar_DZ.UTF-8 UTF-8

and for cat /etc/locale.conf is:

LANG=ar_DZ.UTF-8
LC_ADDRESS=ar_DZ.UTF-8
LC_IDENTIFICATION=ar_DZ.UTF-8
LC_MEASUREMENT=ar_DZ.UTF-8
LC_MONETARY=ar_DZ.UTF-8
LC_NAME=ar_DZ.UTF-8
LC_NUMERIC=ar_DZ.UTF-8
LC_PAPER=ar_DZ.UTF-8
LC_TELEPHONE=ar_DZ.UTF-8
LC_TIME=ar_DZ.UTF-8

Thanks for the information. Can you also post the output of:
locale -a

and if ar_DZ.UTF-8 is in the output, see if issuing the following command fixes the problem:
sudo locale-gen

Thanks for the information. Can you also post the output of: locale -a and if ar_DZ.UTF-8 is in the output, see if issuing the following command fixes the problem: sudo locale-gen

The output of locale -a is :

ar_AE.utf8
ar_BH.utf8
ar_DZ.utf8
ar_EG.utf8
ar_IN
ar_IN.utf8
ar_IQ.utf8
ar_JO.utf8
ar_KW.utf8
ar_LB.utf8
ar_LY.utf8
ar_MA.utf8
ar_OM.utf8
ar_QA.utf8
ar_SA.utf8
ar_SD.utf8
ar_SS
ar_SS.utf8
ar_SY.utf8
ar_TN.utf8
ar_YE.utf8
C
C.utf8
en_AG
en_AG.utf8
en_AU.utf8
en_BW.utf8
en_CA.utf8
en_DK.utf8
en_GB.utf8
en_HK.utf8
en_IE.utf8
en_IL
en_IL.utf8
en_IN
en_IN.utf8
en_NG
en_NG.utf8
en_NZ.utf8
en_PH.utf8
en_SC.utf8
en_SE.utf8
en_SG.utf8
en_US.utf8
en_ZA.utf8
en_ZM
en_ZM.utf8
en_ZW.utf8
POSIX

after running the command sudo locale-gen nothing changed