I can see the likelihood of a new ruling elite insisting that all government documents are in their own language, and possibly that official business be conducted in it.

I think it was pretty recent (in the last 10 years) that Parliament abandoned the practice of writing new English laws on vellum, in Norman French. Can you imagine that? On vellum. In Norman French!!! That's what I love about this country, we have the best anachronisms (or we did before New Labour got into power anyway... I don't think it's even compulsory to practise archery on a Sunday nowadays)!