The simples solution would be to install the MediaWiki stack twice. However, with this solution, you will have duplicated web and database servers so each of them should be in different ports.
There is another option but it will require several manual changes. You will need to install a LAMP stack, install the MediaWiki module on top of it, rename the installation and database name and finally install the MediaWiki module again.
The steps for the second approach are documented for Joomla! in this link, but it should be very similar for MediaWiki.
I hope it helps,