Foreign law is entirely irrelevant to the exploration and determination of the Constitution’s meaning, unless. . . well unless you think the Constitution has no real meaning and is a trampoline from which the judges may launch themselves into all manner of argument, investigation, and philosophical debate. If you think it is impossible or simply foolhardly to determine what the Constitution means (and think your job is to look for intriguing ideas, interesting notions, and cultural trends to impose on the populace) then foreign law, or novels for that matter, are perfectly relevant.
But which law? Saudi Arabian on women’s rights? I think Justice Ginsburg would recoil in horror. Irish or Italian law on separation of church and state? Preposterous. It becomes obvious that foreign law soon devolves into a sort of grocery shelf from which individual justices can pluck whatever looks “good” and disregard the rest.
I think I have a novel I’d like Justice Ginsburg to use in her next foray into non-USA sources for jurisprudential input.
Or maybe she could just use the Torah, definitely a source of input from a foreign Court.