Subdomains, multilanguage

Hello there!
I’ve installed wordpress as multisite, with subdomains (registrations opened).
I’d like it to be multilanguage, i’ve read http://wpmututorials.com/how-to/localization/ and installed language packs, which is fine to have the panels and sites with the language we want.

However i’d like to have different portals, let’s say http://www.site.com for english, fr.site.com for french it.site.com for italian.. with the same database. This is possible if i create fr.site.com set it as french.. But.. i’d like the signup page to be in french too, wp-signup.com redirects back to www.

What’s the best way to have such localized portals? (like wordpress.com).
Different installs with same database, and maybe symlink’ing the plugins/themes/blog.dir folders?
Or some kind of trick to have the signup page on other subdomains?

Anyone knows how wordpress.com does?

Any help is appreciated, i’ve searched for information about it for days..!
Thanks!