Client: i18n (#8972)

* wip: client: i18n

* remove maxAge from cookies to get same expiration ad localStorage

* set cookies expiration to 10 years

* moment: load translations in browser, moment: only load necessary data, remove jquery, remove bluebird

* ability to change language

* fix logout

* add some requiresLogin: false to static pages

* fix tests

website/server/controllers/api-v3/i18n.js

@@ -0,0 +1,46 @@
+import {
+  translations,
+  momentLangs,
+  availableLanguages,
+} from '../../libs/i18n';
+import _ from 'lodash';
+
+const api = {};
+
+function geti18nBrowserScript (language) {
+  const langCode = language.code;
+
+  return `(function () {
+    if (!window) return;
+    window['habitica-i18n'] = ${JSON.stringify({
+      availableLanguages,
+      language,
+      strings: translations[langCode],
+      momentLang: momentLangs[language.momentLangCode],
+    })};
+  })()`;
+}
+
+/**
+ * @api {get} /api/v3/i18n/browser-script Returns a JS script to make all the i18n strings available in the browser
+ * under window.i18n.strings
+ * @apiDescription Does not require authentication.
+ * @apiName i18nBrowserScriptGet
+ * @apiGroup i18n
+ */
+api.geti18nBrowserScript = {
+  method: 'GET',
+  url: '/i18n/browser-script',
+  async handler (req, res) {
+    const language = _.find(availableLanguages, {code: req.language});
+
+    res.set({
+      'Content-Type': 'application/javascript',
+    });
+
+    const jsonResString = geti18nBrowserScript(language);
+    res.status(200).send(jsonResString);
+  },
+};
+
+module.exports = api;