You should not be passing file names in different encodings because other apps won't be able to display them properly. There should be one standard encoding for file names. It would also help with things like looking up a name ignoring case and extra spaces.
I mean, I agree there _should_ be one standard encoding, but the Unix API (to pick the example I'm closest to) predates these nuances. All it says is that filenames are a string [of bytes] and can't contain the bytes '/' or '\0'.
It is good for an implementation to enforce this at some level, sure. MacOS has proved features like case insensitivity and unicode normalization can be integrated with Unix filename APIs.
