Studio (2021) offers 3 different variants of Spanish (not assigned to another region). I'm trying to work out what they actually mean:

es-Es = Spanish (International Sort)
es-x-int-SDL = Spanish (International)
es-x-mo-SDL = Spanish (Spain)

Ok. es-ES is the only fully qualified iso code (or rather IETF BCP 47) , and defines it as Spanish (Spain). Studio just assumes the sort order by convention.

es-x-mo-SDL is also Spanish (Spain), so one would expect it to be the traditional sort counterpart. But it is called Modern, and from what I could find, the sort orders International and Modern are used interchangeably. 

And there is es-x-int-SDL. Here, the International does not refer sort order. Is it then a sort of world wide, region agnostic Spanish?

And for a bit of fun, MultiTerm happily lives in a world of its own, throwing in five variants, partly contradicting Studio...

es =  Spanish
es-es = Spanish (Spain)
es-em = Spanish (International Sort)
es-int-sdl = Spanish (International)
es-mo-sdl Spanish (Modern)

But for now I'd be happy to just learn what exactly the Studio variants mean.

Cheers, Gerhard