I see the new update with the WPML Certificated.But the language selector that i had in the menu has disappeared, although it is enable. Do you know anything about this?

Yes we disabled the language selector in the header menu due to responsive issues. We let our users to customize it and styling it as they see fit. To re-enable it you just need to add

.menu-item-language {
    display: block !important;

in Customizer -> Additional CSS