I'd say that legal language, at least in America, is absolutely well within the bounds of natural language, with all the ambiguity that implies. Certainly lawyers have their own jargon and "terms of art" that sound unfamiliar to the uninitiated, but so do airplane pilots and sailors and auto mechanics. It's still not mathematics.

There are a lot of legislators and judges, and they don't all use words in exactly the same ways. Over time, the processes of binding precedent and legal authority are supposed to resolve the inconsistencies within the law, but the change is slow. In the meantime, statutes keep on changing, and human beings keep on presenting courts with new and unexpected problems. And judges and legislatures are only people within a society and culture which itself changes. Our ideas about "moral turpitude" and "public policy" and what a "reasonable man" (or person) would do are subject to change over time. In this way, the language of the law is like a leaky boat that is being bailed out by the crew. It's not a closed system.