Best to send a letter. Preferably in Croatian, if not, at least few lines. I am pretty sure that Robert Jerin's site might have a sample letter.www.croatia-in-english.com/rj/index.html
More and more young people are learning English and you might get a reply in English but still a good idea to send a letter in native tongue. Less trouble for them as they do not have to find a translator and thus a quicker reply to you. My observation.