How can I manage extensions for MediaWiki?

What type of hardware are you using: VPS bought online
What YunoHost version are you running: 12.0.17 (stable)
What app is this about: MediaWiki

Describe your issue

I want to use the Extension:ParserFunctions - MediaWiki and according to my Special:Version it is not installed.
In ./var/www/mediawiki/extensions however I see a folder called ParserFunctions and it seems to have all the necessary contents.
There are two locations for a LocalSettings.php file.
If I add wfLoadExtension( ‘ParserFunctions’ ); to ./etc/yunohost/apps/mediawiki/conf/LocalSettings.php nothing happens. If I add it to ./var/www/mediawiki/LocalSettings.php then the wiki doesn’t load anymore.

Usually ParserFunctions should be preinstalled, but a simple test string {{#ifeq: 1 | 1 | yes | no}} just returns the test string. It should return “yes”.

Share relevant logs or error messages

Looks like there’s a problem with this site
Version - ChillerWiki might have a temporary problem or it could have moved.
Error code: 500 Internal Server Error
The site could be temporarily unavailable or too busy. Try again in a few moments.

Even if I add $wgShowExceptionDetails = true; into LocalSettings.php I only get the error message above.

any ideas?