Then it shouldn't be mandatory but instead voluntary. You could probably encourage somehow though.

But then you can face potential outside presures against learning it (by the social groups one is integrated in) aswell. "Več kot znaš, več veljaš" (the more you know the more you're worth) is a popular saying here and quite true too. If one must learn foreign languages it also wouldn't harm to learn a major own or neighbouring dialect, which imo comes even more handy. :)