Filter: pll_preferred_language not working

excuse me in advance for the language errors (I speak French)

I need more information about this filter, I’m trying to set up a selection of the language by the user in his preferences on my site.

I save the language code in a user meta

I would like to use this filter so that the language is defined by this meta in priority but I can’t get this filter to work

here is my code:

add_filter('pll_preferred_language', 'set_preferred_language_to_user_meta', 10, 2);
function set_preferred_language_to_user_meta($slug, $languages) { 
if(current_user_is_logged()){
    $locale = get_user_meta(get_current_user_id(), 'locale', true);
    return empty($locale) ? ($slug === false ? 'en' : $slug) : $locale;
  }
return $slug === false ? 'en' : $slug;
}

The meta contains “fr” or “en” but the result is that the language defaults to “fr” no matter what is in my meta

The page I need help with: [log in to see the link]