Use the i18n tag for strings that can't be translated.

remoting/webapp/l10n.js

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 var l10n = l10n || {};
 
 /**
  * Localize an element by setting its innerText according to the specified tag
  * and an optional set of substitutions.
  * @param {Element} element The element to localize.
  * @param {string} tag The localization tag.
  * @param {(string|Array)=} opt_substitutions An optional set of substitution
  *     strings corresponding to the "placeholders" attributes in messages.json.
  * @param {boolean=} opt_asHtml If true, set innerHTML instead of innerText.
  *     This parameter should be used with caution.
  * @return {boolean} True if the localization was successful; false otherwise.
  */
 l10n.localizeElementFromTag = function(element, tag, opt_substitutions,
                                        opt_asHtml) {
   var translation = chrome.i18n.getMessage(tag, opt_substitutions);
-  if (translation) {
-    if (opt_asHtml) {
-      element.innerHTML = translation;
-    } else {
-      element.innerText = translation;
-    }
+  if (!translation) {
+    console.error('Missing translation for "' + tag + '":', element);
+    translation = tag;  // Make errors more obvious
+  }
+  if (opt_asHtml) {
+    element.innerHTML = translation;
   } else {
-    console.error('Missing translation for "' + tag + '":', element);
+    element.innerText = translation;
   }
   return translation != null;
 };
 
 /**
  * Localize an element by setting its innerText according to its i18n-content
  * attribute, and an optional set of substitutions.
  * @param {Element} element The element to localize.
  * @param {(string|Array)=} opt_substitutions An optional set of substitution
  *     strings corresponding to the "placeholders" attributes in messages.json.
@@ skipping 38 matching lines @@
         break;
       }
     }
     l10n.localizeElement(element, substitutions, substitutions.length != 0);
     // Localize tool-tips
     // TODO(jamiewalch): Move this logic to the html document.
     var editButton = document.getElementById('this-host-rename');
     editButton.title = chrome.i18n.getMessage(/*i18n-content*/'TOOLTIP_RENAME');
   }
 };