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

All attributes support only one language, so I believe you should define only one language; the most important language should be set. This can’t be done if you have multiple languages on a single document, so here is the info to solve your problem:

The lang and xml:lang attributes do not allow you to assign multiple languages to a single document. So if you’re writing a Web page with multiple languages you have two options:

1. Define a primary language with the lang attribute, and then call out the secondary language(s) with lang attributes on elements in the document

2. Define lang in the specific sections of the document as needed:

   <div lang="fr-CA" xml:lang="fr-CA">
   Canadian French content...
   </div>
   <div lang="en-CA" xml:lang="en-CA">
   Canadian English content...
   </div>
   <div lang="nl-NL" xml:lang="nl-NL">
   Netherlands, Dutch content...
   </div>
   

I have some multiple-language pages and I do use the 2nd option.

You might want to read http://www.w3.org/TR/2007/NOTE-i18n-html-tech-lang-20070412/#ri20060630.133619987