Currently there's no information on which version of MediaWiki and PHP Extension:SmiteSpam supports. Should figure this out and edit the wiki page to reflect this.
Additional details for Google-Code-In-2015
If you can test the extension on PHP 5.3.3 and MediaWiki 1.23 and it works, then we're done here. I don't intend to support any versions older than those. However, at least one user mentioned that the extension does not work on these versions.
I can confirm that it works on PHP 5.5.9 and git master.
The most direct way would be to run the extension on PHP 5.3.3 and MW 1.23 and see what exactly fails. After we know what the issue is, we can figure out from what version the failing PHP feature or failing MW feature was available.
Other options include:
- Run an automated checker, such as the PHP_CodeSniffer standard from https://github.com/wimg/PHPCompatibility
- Read the release notes for MW versions, or find a list of common issues encountered on upgrading (such as PHP's array() vs  syntax) - both for PHP and for MW and then look for those issues in the code