Clarify whether $orderby and string comparison with ge, gt, le, lt is language-specific

Alphabetical order of modified letters (â, ö, ñ, ...) is language-specific, see e.g.  https://en.wikipedia.org/wiki/Alphabetical_order#Language-specific_conventions

Currently it is neither specified how this must be implemented, nor is it explicitly left to the specific service.

Also alphabetical order typically places the uppercase variant of a letter next to its lowercase variant, i.e. A, a, AA, Aa, aa, AAA, AAa, ...