Tamara-IT on "Need advice on multilingual solutions"

Hello!
This is my problem:
I have to setup an english version of my website (single site install - original language is Italian). I would prefere not to go on with a multisite install but I'll do, if it will be absolutely needed. The thing I'd like most would be that users could be directed automatically on IT or EN version, depending upon their settings (italians on IT, rest of the world on EN). But I guess this requires MultiSite.
Alternatively, users enter the site, which has its default language, see a link to switch and they switch.
In both cases, I need that every post/page has its SEO plugin fields both for IT and EN, so I guess I need something that creates a different DB entry for every post/page and something that makes easy to add/delete language versions.
What is your preferred method to manage multilingual sites?
Thanks!