diff -u b/includes/locale.inc b/includes/locale.inc
--- b/includes/locale.inc
+++ b/includes/locale.inc
@@ -152,7 +152,7 @@
   if (preg_match_all('@(?<=[, ]|^)([a-zA-Z-]+|\*)(?:;q=([0-9.]+))?(?:$|\s*,\s*)@', trim($_SERVER['HTTP_ACCEPT_LANGUAGE']), $matches, PREG_SET_ORDER)) {
     // Load custom mappings to support browsers that are sending non standard
     // language codes.
-    $mappings = language_get_browser_drupal_langcode_mappings();
+    $mappings = variable_get('locale_language_mappings', array());
     foreach ($matches as $match) {
       if ($mappings) {
         $langcode = strtolower($match[1]);
diff -u b/modules/locale/locale.install b/modules/locale/locale.install
--- b/modules/locale/locale.install
+++ b/modules/locale/locale.install
@@ -226,6 +226,21 @@
 }
 
 /**
+ * Set default mappings for Chinese languages.
+ */
+function locale_update_7006() {
+  language_set_browser_drupal_langcode_mappings(array(
+    'zh-tw' => 'zh-hant', // Taiwan Chinese in traditional script
+    'zh-hk' => 'zh-hant', // Hong Kong Chinese in traditional script
+    'zh-mo' => 'zh-hant', // Macao Chinese in traditional script
+    'zh-cht' => 'zh-hant', // traditional Chinese
+    'zh-cn' => 'zh-hans', // PRC Mainland Chinese in simplified script
+    'zh-sg' => 'zh-hans', // Singapore Chinese in simplified script
+    'zh-chs' => 'zh-hans', // simplified Chinese
+  ));
+}
+
+/**
  * @} End of "addtogroup updates-7.x-extra".
  */
 
@@ -262,6 +277,7 @@
   variable_del('javascript_parsed');
   variable_del('locale_field_language_fallback');
   variable_del('locale_cache_length');
+  variable_del('locale_language_mappings');
 
   foreach (language_types() as $type) {
     variable_del("language_negotiation_$type");
diff -u b/modules/locale/locale.module b/modules/locale/locale.module
--- b/modules/locale/locale.module
+++ b/modules/locale/locale.module
@@ -1095,7 +1095,6 @@
   }
 }
 
-
 /**
  * Returns language mappings between browser and Drupal language codes.
  *
diff -u b/modules/locale/locale.test b/modules/locale/locale.test
--- b/modules/locale/locale.test
+++ b/modules/locale/locale.test
@@ -1640,4 +1640,6 @@
 class LocaleBrowserDetectionTest extends DrupalWebTestCase {
 
+  public static $modules = array('locale');
+
   public static function getInfo() {
     return array(
@@ -1647,6 +1649,10 @@
     );
   }
 
+  function setUp() {
+    parent::setUp('locale');
+  }
+
   /**
    * Unit tests for the locale_language_from_browser() function.
    */