more documentation for I18n JS utility

static/js/services/i18n.js

@@ -1,8 +1,18 @@
 (function() {
   'use strict';
 
-  // Global I18n registry that stores and serves translations.
+  /**
-  // Each translation must have a unique ID.
+   * I18n
+   *
+   * This module stores and serves translated strings, according to the users language settings.
+   *
+   * Translations are stored in /messages/frontend/*.msg.
+   *
+   * To make additions to any of these files accessible to JavaScrip Utilities
+   * you need to add them to the respective *.msg file and to the list of FrontendMessages
+   * in /src/Utils/Frontend/I18n.hs.
+   *
+   */
   window.I18n = (function() {
 
     var translations = {};
@@ -19,7 +29,7 @@
 
     function getTranslation(id) {
       if (!translations[id]) {
-        return '(translation missing for »' + id + '«)';
+        throw new Error('I18N Error: Translation missing for »' + id + '«!');
       }
       return translations[id];
     }