Thread:Project:Support desk/PHP errors when trying to upgrade

I'm attempting to update our version of Mediawiki. I've been following the upgrade instructions and have uploaded all of the new files to the server. When I go to /mw-config/index.php, I see this error:

Fatal error: Access to undeclared static property: LanguageConverter::$languagesWithVariants in ..../public_html/help/includes/User.php on line 1369

I've searched all over and have not found any references to this error.

Any advice would be greatly appreciated.