Since 5.0, Qt has its won internal mimedatabase, which is used as a fallback on Windows and OSX. Since the mechanism to extend the contents needs a) updatemimedatabase, which is a pig to build on Windows, and b) needs the XDG system for adding paths, which is alien on Windows and OSX, it's hard to extend the database with the extra mimetypes Krita needs to know about.

This wrapper has a fallback for mimetypes that Qt doesn't know about, and which we cannot reliably add to the share/mime on Windows and OSX. For now, these patterns are hard-coded in KisMimeDatabase, but they should come from the import/export plugins. The problem is that they then should be defined in the .json files, and those aren't translated yet.

It's also a bit weird to depend on this huge, generic thing when all we need to do is load and save the file types we already know about, so in future when we can read all relevant information from the import/export plugins we might even want to drop using QMimeDatabase.