language-dropdown.js

const addUrls = (function() {
  const dropdown = window.document.querySelectorAll(".language-dropdown")[0];

  // run only, when there is the language dropdown (not on 404 and password page)
  if (dropdown !== null) {
    const links = dropdown.querySelectorAll(".dropdown-link");
    const origin = window.location.origin; // https://www.example.com
    let path = window.location.pathname; // /post/blogpost-name-lorem
    let fullUrl;
    const defaultLanguage = "en"; // default language does not have lang code in url (e.g. example.com is default english) & will not be added for redirection

    // If Homepage dont do anything otherwise change links
    if (path === "/" || path === "/de" || path === "/fr") {
      return false;
    } else {
      // go through every link and get the language code from the language dropdown
      Array.prototype.forEach.call(links, function(el, i) {
        let attr = el.getAttribute("href");

        if (attr === "/" || attr === "/" + defaultLanguage) {
          attr = "";
        }

        const regexLang = /\/(:?[\w]{2})\//g; // should discover just the "/de/" or "/en/" or "/fr/" or any 2 characters between slashes, but only the first
        const arrPath = regexLang.exec(path);
        if (arrPath) {
          path = path.replace(regexLang, "/");
        }

        const fullUrl = origin + attr + path; // e.g. https://www.example.com/de/example-site
        // If Blog / or Blog Category, then add get param to set the language (because all translated content is on one page - because of collections)
        const arrParam =
          /magazin/g.exec(location.pathname) ||
          /\/article|post|artikel\//g.exec(location.pathname) ||
          /\/category|cat|kategorie\//g.exec(location.pathname);

        if (arrParam) {
          const langPath = attr.replace("/", ""); // cut the / from the default href of the link
          //const newPath = origin + path + "?lang=" + langPath; // make a absolute path out of it
          const newPathMagazine = origin + attr + "/magazine"; // make a absolute path out of it
          el.setAttribute("href", newPathMagazine); // set the attribute

          if (attr === "/de") {
            el.setAttribute("href", origin + attr + "/magazin"); // set the attribute
          }
        } else {
          // Check if the requested site exists in the language and set it to e.g  /en/delivery otherwise do nothing and redirect to /en
          const request = new XMLHttpRequest();
          request.open("GET", fullUrl, true);
          request.onload = function() {
            if (request.status >= 200 && request.status < 400) {
              // Site is translated, to update the links

              let newPath = attr + path; // make a relative path out of it
              el.setAttribute("href", newPath);
            } else {
              // do nothing because the site is not there in the language
            }
          };
          request.onerror = function() {
            // do nothing because the site is not there in the language
          };
          request.send();
        }
      });
    }
  }
})();