Website Quality Alert
More than one text-processing content language defined
The lang and xml:lang attributes of the html tag allow only one text-processing language to be specified.
Whereas the HTML meta tag specification and the HTTP header content language specification allow a list of languages to be given for the language(s) of the document's intended audience, the text-processing language must be unique.
is incorrect, and
<html xml:lang="en" xmlns= "http://www.w3.org/1999/xhtml">
According to the W3C Internationalization Best Practices, language information is useful for things such as authoring tools, translation tools, accessibility, font selection, page rendering, search, and scripting. In practice, we see that localized search engines (such as google.it) make use of language information, so that missing or incorrect information may have a negative impact of search engine ranking. It is also likely to affect site visitors who use screen readers or spell checkers, in case an input from the user is expected.
Always specify one text-processing language in the html attribute, and only if necessary and helpful specify additional languages in the HTML meta tag specification or in the HTTP header content language specification.