Dune was the book that switched me to reading in English when I was around 14 or 15. I've always loved science fiction, but until that point, I'd read it only in Danish. This was a problem, because the Danish market is so small (we're only around 5½ million Danes) that very little sci-fi is translated into Danish. Also, Danish is not a good language for sci-fi (in my opinion) or for much of anything, for that matter.
Anyway, my uncle died, and I inherited a box of his old books, among them Dune in English. I'd heard about it, and thought what the hell, I'd give it a go, even though I'd never read a whole book in English yet at that time, although my English was very good. I never looked back. I went out and got the rest of the series soon after (this was long before the new books by Brian Herbert and Kevin Anderson), and I've been reading almost exclusively in English ever since.