If you really want different sites for each country, you would have to use multiple Zenphoto installations. You can't have one Zenphoto installation for multiple sites.
If you would be okay with just one site, you might be able to use the localization built into Zenphoto for what you want. There is an option to use whichever language the user's browser requests (given that Zenphoto has a translation for it).
Also, you can most certainly have multiple users with a single installation.