How popular is the English language in countires such as Croatia, Czech Republic, and Bulgaria?

I'm planning on studying abroad, but I want to go to a country thats not a huge tourist place and where I probably will never go again. I feel that sometime in my life I'll go to England, Germany, France, Spain because their huge tourist attractions and its common to go there on vacation, but how many times have you heard someone say that they are going to Croatia, Czech Republic, or Bulgaria? My point is that when I study abroad, I want it to be at a place where I'll never get a chance to go again. My desire to visit parts of the world I'll probably never go to again brings one problem, language boundaries. If I do travel to one of those three countries, would I find it difficult to find someone who speaks English? What percent of the population speak it? I want to be able to visit these countries but I don't want a language boundary to keep me from enjoying my time. Anything you know on this topic would be greatly appreciated. Thank you!