sh:uniqueLang with upper-/lowercase language

Hi,

I’m wondering how sh:uniqueLang is supposed to work with something like “label1”@en-gb and “label2”@en-GB. 

The SHACL specification doesn’t specify how two language tags should be compared to decide if they are the same. RFC 4646 defines some rules for canonicalisation, which goes much further than just upper- and lowercase. 

https://tools.ietf.org/html/rfc4646#section-4.4 <https://tools.ietf.org/html/rfc4646#section-4.4>

What are people's thoughts on this? 

I guess this would also affect something like sh:equals (eg. “01”^^xsd:int vs. “1”^^xsd:int).

Cheers,
Håvard