--- wp-includes/update.php      2010-08-06 15:33:55.000000000 +0200
+++ wp-includes/update-mine.php 2010-08-06 15:33:49.000000000 +0200
@@ -34,6 +34,8 @@
        }
 
        $locale = apply_filters( 'core_version_check_locale', get_locale() );
+       if ( is_multisite() )
+               $locale = get_site_option( 'WP_LANG' );
 
        // Update last_checked for current to prevent multiple blocking requests if request hangs
        $current->last_checked = time();