The Ubuntu MATE website has had a clean up and re-organisation:
Part of this initiative allows us to add support for translating the website. Currently, this feature is not ready. If you'd like to be the first to know, and are interested in translating ubuntu-mate.org to your language, please join the @translators group.
In the meantime, if you're hungry for translating other projects, take a look at the Get Involved → Translations page which lists all the projects that ship with Ubuntu MATE: