Inpsyde\MultilingualPress\Core\FrontEnd\AlternateLanguages\HTTPHeaders::send PHP Метод

    public function send()
    {
        $translations = $this->translations->to_array();
        if (!$translations) {
            return false;
        }
        array_walk($translations, function ($url, $language) {
            $header = sprintf('Link: <%1$s>; rel="alternate"; hreflang="%2$s"', esc_url($url), esc_attr($language));
            /**
             * Filters the output of the hreflang links in the HTTP header.
             *
             * @since 3.0.0
             *
             * @param string $header   Alternate language HTTP header.
             * @param string $language HTTP language code (e.g., "en-US").
             * @param string $url      Target URL.
             */
            $header = (string) apply_filters('multilingualpress.hreflang_http_header', $header, $language, $url);
            if ($header) {
                header($header, false);
            }
        });
        return true;
    }