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

The meaning of the Content-Language HTTP header, and hence its meta tag surrogate, is that it declares the languages of the document, or the languages of the intended audience (the relevant RFCs are contradicting), not the languages of some other documents (like translations of the current document). The practical effect of header is small, probably limited to using the first language named as the language of the document, if there is no language information in HTML markup.

To indicate that a document is available in other languages, you can use tags like

See 12.3.3 Links and search engines in HTML 4.01 spec.

There is no guarantee that this will have any effect. It might affect search engines, but not more than a normal link would do. Some old browser versions had commands for selecting alternate versions of a document, based on elements like this, but the feature seems to have been dropped.