[throwaway7767]

> I don't think any backup software actually can do the right thing(tm).

Sure it can. In this case, I'd say treating the filename as a bag of bytes is the correct way to go, as that's the way the OS treats them. Translating filenames between character sets should not be part of a backup systems job.

There are valid setups where different software on the same machine might be running with different character sets for legacy reasons. In that case there is no correct way to handle the filenames as text. But treating it as a bag-of-bytes will always work consistently.

Also, the one purpose of a backup system is to back up the files on the filesystem. If it can't back up some files that the OS considers valid, it's the backup software that failed.