Different languages have different rules for change case (as seen here) or what to do when translitterating to 7-bit ascii, in French, you can mostly drop accents if you need to, in German, you need to transform an umlaut to an e following the vowel. Of course, many languages don't have a way to translitterate to 7-bit ascii.
Sorting of strings is language dependent, but I don't know that there's a defined order for mixed language lists, so I guess user's context works if you're sorting for user purposes, but if you're sorting for machine purposes, you better not use the locale aware sort without telling it a hardcoded locale that doesn't change between localization library versions.
Sorting of strings is language dependent, but I don't know that there's a defined order for mixed language lists, so I guess user's context works if you're sorting for user purposes, but if you're sorting for machine purposes, you better not use the locale aware sort without telling it a hardcoded locale that doesn't change between localization library versions.