diff -Nru drupal-6.26.orig//includes/language.inc drupal-6.26/includes/language.inc
--- drupal-6.26.orig//includes/language.inc	2012-05-02 13:36:16.000000000 -0300
+++ drupal-6.26/includes/language.inc	2012-08-29 15:04:39.000000000 -0300
@@ -79,7 +79,7 @@
       // The language part is either a code or a code with a quality.
       // We cannot do anything with a * code, so it is skipped.
       // If the quality is missing, it is assumed to be 1 according to the RFC.
-      if (preg_match("!([a-z-]+)(;q=([0-9\\.]+))?!", trim($browser_accept[$i]), $found)) {
+      if (preg_match("!([a-z-]+)(;q=([0-9\\.]+))?!i", trim($browser_accept[$i]), $found)) {
         $browser_langs[$found[1]] = (isset($found[3]) ? (float) $found[3] : 1.0);
       }
     }