Cache translations.

Fixes: #1158

static/js/src/main.js

@@ -4,6 +4,8 @@
     var i18n = window.i18n = require('i18next');
     var XHR = require('i18next-xhr-backend');
     var lngDetector = require('i18next-browser-languagedetector');
+    var Cache = require('i18next-localstorage-cache');
+
     var backendOptions = {
         loadPath: '/static/locale/__lng__/translations.json'
     };
@@ -15,8 +17,14 @@
         htmlTag: document.documentElement
     };
 
+    var cacheOptions = {
+        enabled: true,
+        prefix: page_params.server_generation + ':'
+    };
+
     i18n.use(XHR)
         .use(lngDetector)
+        .use(Cache)
         .init({
             nsSeparator: false,
             keySeparator: false,
@@ -25,7 +33,8 @@
                 suffix: "__"
             },
             backend: backendOptions,
-            detection: detectionOptions
+            detection: detectionOptions,
+            cache: cacheOptions
         }, function () {
             var i;
             initialized = true;