So, I have three sites running, english.blog.com, norwegian.blog.com and swedish.blog.com. They are connected through the plugin. So, whenever I go to “New post” on any one of those sites, I get fields for translation into the other languages as well (if I want to use them, I can still write a post in just one language if I want to) .

I guess that you could use such a plugin to accomplish some of the things you want.