A filter allowing to output a shorter language slug instead of a language name in Polylang plugin on WordPress.

Language-slug-instead-of-name-in-PolyLang-WordPress

// put this in functions.php:
if ( ! function_exists( 'tco_switcher_language_name' ) ) :
    function tco_switcher_language_name($args = '') {
      $args['display_names_as'] = 'slug';
      return $args;
    }
    add_filter('pll_the_languages_args','tco_switcher_language_name');
endif;