Automatically determine locale from DocumentMetadata

[d-e-n-n-i-s-t]

I think it'd be great if siunitx could read the locale setting of a document automatically, if it's set via \DocumentMetadata{lang=de-DE}, for example. I know \DocumentMetadata user-input is not checked for errors, but couldn't this be done in the package? Exactly like it's being done right now
Babel started doing it like that for a week now (25.8 introduced this)

There are some languages without locales, I don't know how to handle those cases though

[josephwright]

As detailed in the manual, the locale key in siunitx is about the typographic tradition in use for typesetting a document, not the language the document is written in.

[d-e-n-n-i-s-t]

not the language the document is written in.

lang= doesn't only specify the language the document is written in. You can specify both a language and a locale. In the case of en-US and en-GB, the language would be English for both, but the locale is different.

As far as I understand, that second part (-US or -GB) is logically the exact equivalent to the locale we set in siunitx's package options. If there would be a scenario in which you'd want a different locale only for siunitx, you'd still be able to override the global locale just for siunitx with the package option