I would probably decline an invitation to a wedding where I was expected to cover my plate.
I also think that if you plan on having a traditional wedding (Chinese, Croatian, etc.) that it might be a good idea to include that info in the invite. Whether you just point out that it's going to follow the traditions of that culture or take an extra steps and include information for where someone can go to read about it. It won't guarantee that every guest will bring something that's appropriate for the tradition, but I do think some of the responsibility is going to fall on the couple if they have specific expectations about the gifts.
I see your point, but I wouldn't do it. How would you word it? "The honor of your presence is requested at our traditional Croatian wedding"? I would find that confusing, and possibly even a bit arrogant, as if their wedding were somehow more correctly traditional than other people's. And no matter how you'd word it, it would also look to me like exactly what it really is: trying to direct gift-giving toward cash, which, like any other push toward a gift, is rude no matter what, the same as if they'd put "cash gifts requested" on the invitation. That's my problem with the bolding: whether or not there is a traditional gift in the couple's community or culture, they are rude to ask or even hint for it unless and until asked what they'd like. Whatever gift people give them, unless it is something the giver knew to be outright offensive, is by definition a lovely surprise.
That a polite guest tries to ascertain and, if possible, conform to what is considered appropriate in the couple's community, does not equal permission for the couple to try to push them to do so or be anything but gracious if they don't -- just like the existence of a registry does not make it rude to choose something elsewhere. A gift is always voluntary and it is always the giver's choice, not the recipients'.