Ticket #18741: 18741.patch

wp-admin/includes/update-core.php

@@ -384 +384 @@
                         $lang_dir = WP_CONTENT_DIR . '/languages';
 
                 if ( !@is_dir($lang_dir) && 0 === strpos($lang_dir, ABSPATH) ) { // Check the language directory exists first
-                        $wp_filesystem->mkdir($to . str_replace($lang_dir, ABSPATH, ''), FS_CHMOD_DIR); // If it's within the ABSPATH we can handle it here, otherwise they're out of luck.
+                        $wp_filesystem->mkdir($to . str_replace(ABSPATH, '', $lang_dir), 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
                 }