Multisite, a site per country.

Hi there, I´m planning a site and I really don´t know what can be the right approach. The basics of my project are:

2 countries, 2 provinces in each country
Users register choosing country and province (where they live) and then create a business referenced to both country and province.
Once the business is created, users can send messages to any business (or search for a business) in other provinces of any of both countries.

Until here I know the options, I can solve it using OG, entity references, etc.

One of my problem is that users registered in -let´s say- UK should access a site in English while the ones registered in Spain will access a site in spanish and I don´t know how to split the translations depending of the group the user is registered in: in other words, if user A has registered in UK, sees the site in english. Can you do this with OG? with E.Reference, other? My first thought is NO you can´t.

So, my next approach should be something like to build a multisite? ...where each site will represent a country with it´s provinces, users and businesses... and a language per site? But then my question is how should it the architecture be to allow a user in SITE 1 look for a user/business in SITE 2.

I´m new in "multisiting" so if anyone can correct me and/or point me in the right direction I would be very appreciated.

Thanks so much.

Nico