Its caused by the following line in [[ar:MediaWiki:Common.css]]

/*External link color transition
**http://ar.wikipedia.org/w/index.php?diff=10832343&oldid=10832341*/a.external{-o-transition:color .2s ease-out, background 1s ease-in;-ms-transition:color .2s ease-out, background 1s ease-in;-moz-transition:color .2s ease-out, background 1s ease-in;-webkit-transition:color .2s ease-out, background 1s ease-in;transition:color .2s ease-out, background 1s ease-in;padding:0!important;background:none!important;direction:rtl!important;}

(Specifically the background:none!important part tells browsers to not show the icon, which is considered part of an external links "background")

MediaWiki:Common.css is controlled by local admins, not us, so closing this bug as invalid.

SyrianEng wrote:

thank you