hi Carlo,
as i understood, you will have 5 different sites, one of theese in two languages, is it?
In my opinion you should set 5 different databases that contain the different content, and one of theese will have two translations of the content (so the structure will be the same). This means that you will have 5 sites with its 5 admin interfaces. That will make 10 siteaccesses. That's the way i would do it, but maybe it's not the best.
First you should search in the documentation and forums how to set multiple sites with one installation, and then how to set multilingual sites.
I've got two sites with different databases in my installation and one supports two languages, i'm not an expert at all, but i can give you a little help if you decide to go on with it.
I wouldn't setup different databases. Too much trouble in the long run in my opinion, but it depends on the situation and might make good sense too.
But you can do this all in one database with different siteaccesses. Create folders for every site you want to do, then create the content inside them. Setup different siteaccesses for every language/site and the right starting URL. You can administrate all through one admin interface or create different admin interfaces for each site if you want.
Obviously you can also mix the different approaches. Make different databases for some sites and keep others in the same database.