Are you sure the text direction is correctly set for Arabic ? Edit the Arabic language, check rtl and resave.
Digging in your html code, I found that the theme has another stylesheet http://alefba.us/polylangtest/en/?pageless=1344489160
The url is badly formed : http://alefba.us/polylangtest/?pageless=1344489160 is expected
It is possible that somewhere in your theme code, something like:
home_url('/') . '?pageless=1344489160'
should be replaced by:
However, it is curious that it works on the Arabic page... (where the url is badly formed too with /ar/ instead od /en/).