code: function(id) {
              if (!$$.App) $$.App = this;
              if (!$$.App._languages) {
                  // Initialise localization.
                  var languages = [],
                  langStyle = document.createElement("style"),
                  children = document.querySelectorAll("[lang]");
                  document.head.appendChild(langStyle);
                  $$.App._langStyle = langStyle;
                  for (var i = 0 ; i < children.length ; i++) {
                      var child = children[i];
                      lang = child.getAttribute("lang");
                      found = false;
                      for (k = 0 ; k < languages.length ; k++) {
                          if (languages[k] == lang) {
                              found = true;
                              break;
                          }
                      }
                      if (!found) {
                          languages.push(lang);
                      }
                  }
                  $$.App._languages = languages;
              }
  
              var that = this, lang, k, found, first, txt;
              languages = $$.App._languages;
              if (id === undefined) {
                  // Return current language.
                  lang = $$.lang();  // localStorage.getItem("wtag-language");
                  if (!lang) {
                      lang = navigator.language || navigator.browserLanguage || "fr";
                      lang = lang.substr(0, 2);
                  }
                  $$.lang(lang);
                  // localStorage.setItem("wtag-language", lang);
                  return lang;
              } else {
                  // Set current language and display localized elements.
                  found = false;
                  for (k = 0 ; k < languages.length ; k++) {
                      if (languages[k] == id) {
                          found = true;
                          break;
                      }
                  }
                  if (!found) {
                      id = languages[0];
                  }
                  txt = "";
                  first = true;
                  for (k = 0 ; k < languages.length ; k++) {
                      lang = languages[k];
                      if (lang != id) {
                          if (first) {
                              first = false;
                          } else {
                              txt += ",";
                          }
                          txt += "[lang=" + lang + "]";
                      }
                  }
                  $$.App._langStyle.textContent = txt + "{display: none}";
                  $$.lang(id);
                  //localStorage.setItem("wtag-language", id);
              }
          }
docs: Return or set the current language.
  @memberof WTag