hreflang tag in head

i did the search and found this from Yigit: https://kriesi.at/support/topic/hreflang-tags/

add_action('wp_head', 'ava_add_your_stuff');
function ava_add_your_stuff() {
    ?>
<link rel="alternate" hreflang="es" href="http://es.example.com/" />
    <?php
}

but it didn’t work for me! no code was inserted. WPML placed two hreflang links on the language specific pages but i want to set the x-default link