diff --git a/modules/gallery/helpers/locales.php b/modules/gallery/helpers/locales.php
index 04fa8954..16dda2d7 100644
--- a/modules/gallery/helpers/locales.php
+++ b/modules/gallery/helpers/locales.php
@@ -56,6 +56,9 @@ class locales_Core {
       : array_merge($locales, array($default));
 
     module::set_var("gallery", "installed_locales", join("|", $locales));
+
+    // Clear the cache
+    self::$locales = null;
   }
 
   // @todo Might want to add a localizable language name as well.
@@ -167,7 +170,7 @@ class locales_Core {
       }
 
       // Compare and score requested locales with installed ones
-      $matched_locales = array();
+      $scored_locales = array();
       foreach ($locale_preferences as $requested_value) {
         $scored_locale_match = self::_locale_match_score($requested_value);
         if ($scored_locale_match) {
@@ -175,7 +178,7 @@ class locales_Core {
         }
       }
 
-      usort($matched_locales, array("locales", "_compare_locale_by_qvalue"));
+      usort($scored_locales, array("locales", "_compare_locale_by_qvalue"));
 
       $best_match = array_shift($scored_locales);
       if ($best_match) {
@@ -202,7 +205,8 @@ class locales_Core {
       return $requested_locale_and_qvalue;
     }
     list ($language) = explode("_", $requested_locale . "_");
-    if (isset(self::$language_subtag_to_locale[$language])) {
+    if (isset(self::$language_subtag_to_locale[$language]) &&
+        isset($installed[self::$language_subtag_to_locale[$language]])) {
       return array(self::$language_subtag_to_locale[$language], $qvalue * 0.66);
     }
     return null;
diff --git a/modules/gallery/tests/Locales_Helper_Test.php b/modules/gallery/tests/Locales_Helper_Test.php
new file mode 100644
index 00000000..85b8e206
--- /dev/null
+++ b/modules/gallery/tests/Locales_Helper_Test.php
@@ -0,0 +1,86 @@
+<?php defined("SYSPATH") or die("No direct script access.");
+/**
+ * Gallery - a web based photo album viewer and editor
+ * Copyright (C) 2000-2009 Bharat Mediratta
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+class Locales_Helper_Test extends Unit_Test_Case {
+  static $installed_locales;
+  static $default_locale;
+
+  public function setup() {
+    self::$installed_locales = locales::installed();
+    self::$default_locale = module::get_var("gallery", "default_locale");
+    locales::update_installed(array_keys(locales::available()));
+    module::set_var("gallery", "default_locale", "no_NO");
+  }
+
+  public function teardown() {
+    locales::update_installed(array_keys(self::$installed_locales));
+    module::set_var("gallery", "default_locale", self::$default_locale);
+  }
+
+  public function locale_from_http_request_test() {
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "de-de";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("de_DE", $locale);
+  }
+
+  public function locale_from_http_request_fallback_test() {
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "de";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("de_DE", $locale);
+  }
+
+  public function locale_from_http_request_by_qvalue_test() {
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "de-de;q=0.8,fr-fr;q=0.9";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("fr_FR", $locale);
+  }
+
+  public function locale_from_http_request_default_qvalue_test() {
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "de-de;q=0.8,it-it,fr-fr;q=0.9";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("it_IT", $locale);
+  }
+
+  public function locale_from_http_request_lang_fallback_qvalue_adjustment_test() {
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = ",fr-fr;q=0.4,de-ch;q=0.8";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("de_DE", $locale);
+  }
+
+  public function locale_from_http_request_best_match_vs_installed_test() {
+    locales::update_installed(array("no_NO", "pt_PT", "ja_JP"));
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "en,en-us,ja_JP;q=0.7,no-fr;q=0.9";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("ja_JP", $locale);
+  }
+
+  public function locale_from_http_request_best_match_vs_installed_2_test() {
+    locales::update_installed(array("no_NO", "pt_PT", "ja_JP"));
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "en,en-us,ja_JP;q=0.5,no-fr;q=0.9";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal("no_NO", $locale);
+  }
+
+  public function locale_from_http_request_no_match_vs_installed_test() {
+    locales::update_installed(array("no_NO", "pt_PT", "ja_JP"));
+    $_SERVER["HTTP_ACCEPT_LANGUAGE"] = "en,en-us,de";
+    $locale = locales::locale_from_http_request();
+    $this->assert_equal(null, $locale);
+  }
+}
\ No newline at end of file