Thank you for your reply and for your help Kevin,
Here is the output of the locale command
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$ locale
LANG=en_GB.UTF-8
LC_CTYPE=en_GB.UTF-8
LC_NUMERIC=ar_EG.UTF-8
LC_TIME=en_GB.UTF-8
LC_COLLATE=en_GB.UTF-8
LC_MONETARY=ar_EG.UTF-8
LC_MESSAGES=en_GB.UTF-8
LC_PAPER=ar_EG.UTF-8
LC_NAME=ar_EG.UTF-8
LC_ADDRESS=ar_EG.UTF-8
LC_TELEPHONE=ar_EG.UTF-8
LC_MEASUREMENT=ar_EG.UTF-8
LC_IDENTIFICATION=ar_EG.UTF-8
LC_ALL=
------------------------------------
So, it is set to utf-8 , and even with running the command:
$ aspell dump master arabic --encoding=utf-8
I get the same old result with the non-arabic characters.