I reinstalled the whole amahi now, this time full fedora install 32-bit. Same problem: Mediawiki installs and when trying to open it the same "Internal Error"-Site appears...

Edit: What you mentioned I tried first, but no success.

Installation works now (thanks!), but when trying to open media wiki it shows a site saying: "MediaWiki internal error. Exception caught inside exception handler."...

I have Amahi Express 64 bit fresh installed.

The same here: Media Wiki install hangs showing "Preparing for install" forever.