Comment by necovek

The big one that's often ignored are collation tables: while there's the default in ISO 10646 IIRC, each region-language combo might have their specific overrides (imagine "ss" being sorted as a separate letter in German, and not as after "sr" and before "st", so it would be sa..., sb..., sr..., st..., ssa..., ssb... etc); and then Austrian German might have a different phonebook ordering.