There are specific reasons for language expansion (there are words which mean a very specific thing, which would require an unnecessary word being created if a good one in another language already exists), but every time the UK has sent a significant number of people to one place - India, for example - we end up with a bunch of entirely new words trickling down into everyday usage. What we have at the moment, with the Internet and films from around the world being made available on DVD - is a slow absorption of words and phrases which might as well be considered English, as the use of some of them have shifted from their original context.
Okay, so it might be a bit much to suggest that we are experiencing a major increase in the vocabulary of our language, but it is growing. Ignoring technical and scientific terms, compression of existing words, slang, and acronyms, we've still seen a spectacular number of words from numerous cultures being brought to light in English-language dictionaries in the last decade. I support this embracing of language fully - it's exciting to see people embracing other cultures in this way.