Hi,

You can configure the multiple sites within one instance as follows - http://www.kentico.com/docs/devguide/configuring_multiple_web_sites.htm. These sites will have one DB. What problems do you have? Any details will be helpfull.

Then you can install for each site a separate CMS instance and of course, each of the site will have separate DB.

Regarding to the language - in CMSResources folder you can find the resource files. The Spanish translation of the interface is also present, but it is possible that not all strings in the latest version are translated correctly (http://www.kentico.com/docs/devguide/configuring_web_site_culture.htm).

Best Regards,
Juraj Ondrus