Re: Multi-language edition
I gave some thoughts to this topic and my conclusion so far is, that it would be the best solution to set up a WPMU + Buddypress System for each language. The only thing that would be needed is a Plugin that shares the Userdata between these systems. A user who signed up on your swedish installation of WPMU + Buddypress should be able to use this account for your english version too and so on.
One could do it as on wordpress.com, where wordpress.com is the main website. If You choose a different language, say german (.de) you get redirected to de.wordpress.com and only german content will appear.