If your goal is to reach native-like fluency, there is a huge difference in the amount of time necessary to reach fluency between French and Japanese The US Foreign Service estimates it takes about 600 hours of intense study for a native English speaker to be fluent in French, but to reach that level in Japanese it takes about 2,700 hours of intense study. You have to decide how much time you want to invest. You may have an easier time with French if your native language is Croatian. I am fluent in Russian, another Slavic language, and I know there are some similarities with Romance/Latin languages like French. Japanese is a very high mountain to climb, but not impossible. I'm studying Mandarin right now and making slow progress. But either of those languages is a good choice and would be an asset in many professions.