Chouby on "[Plugin: Polylang] Does not load rtl.css"

Could you male two separate tests ?

1. check "The language is set from content. Posts, pages, categories and tags urls are not modified" in Polylang settings? Check if it is ok.

2. de-activate Polylang and add:

define('WPLANG', 'ar');

in wp-config.php. Check if it is ok.