The MediaWiki script has not been added in the Fantastico auto-installer yet. This is third party software and only its developers decide whether to add a particular part to it or not. We perform regular Fantastico updates and once the MediaWiki is included, you will notice it.

Therefore, only a manual installation is possible. You may follow the instructions here.

Surely, you can always request a free script installation by posting a ticket. You can do this from:

Customers' Area --> Get Support --> Get Script installed