Index: wp-admin/includes/update-core.php
===================================================================
--- wp-admin/includes/update-core.php	(revision 17577)
+++ wp-admin/includes/update-core.php	(working copy)
@@ -367,7 +367,7 @@
 
 	// Custom Content Directory needs updating now.
 	// Copy Languages
-	if ( !is_wp_error($result) && $wp_filesystem->is_dir($from . $distro . 'wp-content/languages') ) {
+	if ( !is_wp_error($result) && is_callable( array($wp_filesystem, 'wp_lang_dir') ) && $wp_filesystem->is_dir($from . $distro . 'wp-content/languages') ) {
 		if ( !@is_dir(WP_LANG_DIR) && 0 === strpos(WP_LANG_DIR, ABSPATH) ) { // Check the language directory exists first
 			$wp_filesystem->mkdir($to . str_replace(WP_LANG_DIR, ABSPATH, ''), FS_CHMOD_DIR); // If it's within the ABSPATH we can handle it here, otherwise they're out of luck.
 			clearstatcache(); // for FTP, Need to clear the stat cache