Following code snippet replaces placeholder menu item from ‘your-menu’ menu.
add_filter( 'wp_nav_menu_items', 'add_item_to_menu', 10, 2 );
function add_item_to_menu( $items, $args ) {
if ( $args->theme_location == 'your-menu' ) {
$link_text = "My Replaced Link Text";
$link_url = "my-replaced-link-url.com";
$items = str_replace( 'lang_placeholder_text', $link_text, $items);
$items = str_replace( 'lang_placeholder_url', $link_url, $items);
}
return $items;
}