Following the modification to "SiteExporter.php" and "SiteImporter.php" to handle "LanguageCode" property, the XSD file was modified as well.
The new XSD file took version 1.1 and replaces the docs/sitelist-1.0.xsd with docs/sitelist-1.1.xsd: http://www.mediawiki.org/xml/sitelist-1.0/ reference must be updated accordingly.
A new HTML page must be created with similar text as the existing one, but with reference to the 1.1 version XSD file as mentioned