Thread:Project:Support desk/Extension for enabling alphabetization of sub-categories under the full Sort Key instead of the first letter of the Sort Key./reply (3)

nope, not in 1.17. Things are always sorted by the entire sortkey, however only the first character is displayed in the sub-headings (in mediawiki core. It would be possible to make an extension similar to the hack that Sidcom links to, but I'm not aware of any such extension existing atm, and if there was one it would probably not be compatible with the recent category collation changes in 1.17).