wordpress how to change website language with polylang

Question

I am using polylang to change the language in frontend. it is working fine. I have two languages in the website. English and arabic.

What I am trying to do is, when(if) user changes the language in front end. The language in the admin panel has to be change too. But I think polylang only changes the language in frontend.

I tried adding this filter to check which language user currently using but it is not working

add_filter('locale', 'wpse27056_setLocale');

function wpse27056_setLocale($locale) {
    if ( is_admin() ) {
       /*
        $currentLanguage  = get_bloginfo('language');
        return $currentLanguage;
        */
        if(is_rtl()){
          return "ar";
       }
      return "en-US";
    }
}

My question is is there any way where I can code to change whole website's language?