We already have Comcode page translation... if you add a second language pack it will ask what language you want to edit a page in. Works for any kind of content in the system, although it only explicitly asks for the pages.

We don't do selecting what language to view individual content items in, it's site-wide, but I can't see that being very useful. Besides, using the side_language block would take you back to where you were after changing the language, so it's almost the same.

I think the current solution is more streamlined than keeping setting things per item, and I wouldn't want two ways of handling it all.