Is there any standards/guidelines/good practices for making websites with support of different content and UI? I'm interesting in articles/tutorials, that cover this topics.

E.g. there going to be website for multiple countries. And user should have possibility to select UI and content languages separately.

I assume that not all content will be translated, so there should be some mechanism for showing "default language" content for specific page. But again, should this "default" be per site, or per country?

E.g. in some countries (Belgium, Finland) there are several official languages. If one language is unavailable, should default be second one, or English? Another example: many people prefer English UI (no mater of their origin), but want local scales (inches, meters) and local services.

I don't care much about programing languages now, just want to understand what users are expected, what should be scope, and what are good practices.