I thought you couldn't use "säger" with written words. Is it different with laws and other written documents vs. words on signs and buildings and such? (or something of the sort)
Yes, säger doesn't mean 'what does it say' as in 'what is written', that is only vad står det. But vad säger lagen does not refer to the written words so much as to the content of it.
So vad står det i lagen means 'what does it say in the law' in the sense of written text, and vad säger lagen means 'what does the law say' as in, like, what does the law tell us about this, what is the law's 'opinion' about this :)
The law is accepted. That's exactly what it says above: what does the law say?
Bearing in mind Arnauti's contribution why is "what is the law" not accepted. It is probably the english which is most commonly used though the official translation is also fine.