files in all FM's with latin names go before cyrillic ones, I guess the same applies to all nonlatin names too.
before this patch the order is something like this: [папка1, fld1, fld2], after: [fld1, fld2, папка1]
Please change the title to a short description, and add a slightly longer description to the Summary section (if necessary).
Also, you need to add some reviewers. A good start would be "Dolphin" and "KDE Applications"
I don't see how this will affect catalan locale since they both use the same set and order of symbols. So catalan speakers won't note the difference.
On the other hand I don't know (I will test) how will this change result for alphabets with diacritic symbols (e.g. czech Č č, Ď ď and so on).
As an another approach editing QCollate is reasonable too.
You are forcing the en_US locale into all sorting. This defeats the purpose of using the locale to sort. I'd suggest you investigate how it works for your own locale and see into making it sort strings as it makes sense for the speakers of your language.
Languages with the same alphabets do NOT sort the same way. Forcing the wrong locale will sort incorrectly. There are all kinds of quirks between languages. For instance ä is close to last in the alphabet in Swedish, but sorted together with a in German.