The demo wiki needs to its PHP upgraded to 7.2.22 to run MediaWiki 1.35. It looks like this requires a newer version of Debian, at least to do it easily. The one we're running now is deprecated so it's probably just as well. We need to figure out how to easiest migrate the current wiki (settings, content and whatnot).
I've manually installed a MediaWiki on https://wikispeech-wiki-dev.wmcloud.org/ with Wikispeech pointing at the speechoid-dev.
It lives in /var/www/html/mediawiki on core master (1.36.x) using a LAMP-installation with an extra memcached. All passwords etc is stored in ~root/passwords.txt
Try installing with Vagrant again, using the new instructions. If it still doesn't work, use the non-Vagrant installation for now.
Regardless, migrate content and configs to the new installation.