you can find documentation on this feature here:
we've recently upgraded the demo-site to use mutlilingual content as well:
we don't have a tool for switching languages through the frontend yet,
but its quite easy to build (set a session-variable etc.).
by the way, we're always looking for translators for the silverstripe interface, and finnish would be really nice addition! if you're interested to help, we'd be glad to hear from you and set you up with an account to our translation-server.