@namespace a url(http://www.example.org/a);
@namespace b url(http://www.example.org/b);
@namespace html url(http://www.w3.org/1999/xhtml);
*|p, *|address, *|q, *|r { display : block ; margin-bottom : 1em }
*|address, *|r { background-color : lime ! important }
div.stub *|*:not([|lang|="foo-bar"]) { background-color : red }

<div class="stub">
<p lang="foo-bar">This paragraph should be unstyled.</p>
<address lang="foo-b">This address should have a green background.</address>
<address lang="foo-barbar-toto">This address should have a green background.</address>
<q xmlns="http://www.example.org/a" lang="foo-bar">This paragraph should be unstyled.</q>
<r xmlns="http://www.example.org/b" b:lang="foo-bar">This paragraph should have a green background.</r>
</div>