Assertion: The browser will recognize a language declared in the HTTP header.

Notes:
In order to tell whether the language information is available, we test a feature, :lang, that makes use of that information in a detectable way. Unfortunately, such features are not uniformly supported across current user agents, and so conclusions must be drawn with care. We run control tests that will raise a flag if :lang is not supported by the user agent - if it is not, that particular test is not valid. If the test proves positive, that should show that the language declaration was recognized.

Note that we are only testing whether a declaration is recognised, not whether it is appropriate (eg. lang attributes in xml documents).