Do we need guidance on comparing language tags and the role of canonicalization?

See a spec reader (not writer) asking for such guidance here

https://lists.w3.org/Archives/Public/public-shacl/2020Sep/0000.html

The answer might be: no, better refer people to RFC 4647. The above thread does not talk about "matching language tags", but that may be part of the reason for the confusion.