Everything I've seen about English and language in general suggests that English, far from declining is growing, but in such a way that you find many different variants, all mutually (to some degree, at least) intelligible. I haven't read Clash of Civilisations (though it is now something I'll look out for) - but I wonder if what was being referred to as the decline of English was the decline of English as a single language, the 'official' language that noone really speaks.
An, just for the record, I'm all for Internationalisation. Reading something in your first language is (usually*) so much more comprehensible than in a second. Even if the native language translation is slightly rough.
(*) Some languages of course have ways of expressing certain concepts that just don't exist in others.
