Define multiple languages in html root element's lang attribute?

Question

I want to determine more than one language for a document, because it\'s available in more than one language. If I use:

Answer 1

What HTML version do you use? In HTML 4.01, your use of Content-Language with multiple languages is valid. In HTML5, it's not.

But even for HTML 4.01, the use of Content-Language for the meta element is not recommended: HTTP headers, meta elements and language information (W3C)