diff --git a/src/static/js/l10n.js b/src/static/js/l10n.js
index 1d232908e..ef8218d3e 100644
--- a/src/static/js/l10n.js
+++ b/src/static/js/l10n.js
@@ -902,7 +902,7 @@ document.webL10n = (function(window, document, undefined) {
   // browser-specific startup
   if (document.addEventListener) { // modern browsers and IE9+
     document.addEventListener('DOMContentLoaded', function() {
-      var lang = document.documentElement.lang || navigator.language;
+      var lang = document.documentElement.lang || navigator.language || navigator.userLanguage || 'en';
       loadLocale(lang, translateFragment);
     }, false);
   } else if (window.attachEvent) { // IE8 and before (= oldIE)
@@ -977,7 +977,7 @@ document.webL10n = (function(window, document, undefined) {
     // startup for IE<9
     window.attachEvent('onload', function() {
       gTextProp = document.body.textContent ? 'textContent' : 'innerText';
-      var lang = document.documentElement.lang || window.navigator.userLanguage;
+      var lang = document.documentElement.lang || navigator.language || navigator.userLanguage || 'en';
       loadLocale(lang, translateFragment);
     });
   }