If we spoke in TM-computable English, what would it look like?
Under reasonable assumptions, there is a TM which can decide whether something is a valid piece of English legalese. We can safely assume that the length of a law is bounded by some finite number $k$, say the number of characters the fastest human reader can read in less than two hundred years. There is then only a finite number of possible strings that might or might not be valid laws. Hence there is a lookup table of finite size that contains for every string of length at most $k$ the correct answer. 

It is not settled whether humans can in fact recognize languages that TM can't recognize, so it's unclear whether the length restriction is truly necessary. See for example this question, or this question.

This is of course a boring answer, because this TM is completely impractical to construct. In actual practice you probably want to restrict yourself to a subset of English that can be parsed by an LL(k) parser (real English is not context-free), or go for a language specifically designed to be easy to understand to both humans and computers. @LukasBarth mentioned Lojban in the comments, but there are a number of such languages (programming languages are another example).