Well google is your friend, I just tried "camping croatia" and this http://www.camping.hr/ turned up. I have been to croatia twice, and older people also speak german. But you will be able to get around with just english ( or more correct american ) The eastern europe countries also learned russian, but avoid that. Most people becomes oysters when russian are spoken. I think they have been vaccinated aginst it.

Croatia is friendly and rather cheap, and also quite clean. If you go in the summer it will be terribly hot. But that you may have found out.