I just don't want garbage file names when sharing a file system between systems that don't agree on the encoding. I was thinking maybe some mount option. I can use ISO-88591 and skip UTF-8. I haven't found a mount option for ext4 or xfs yet.
You could probably write some filter using fusefs, but in practice... I think you should configure the servers / clients to agree on encoding instead. Better supported and shouldn't be that much work.
But it won't allow you to force ISO-8859-1 in this form. However you could filter out non-ASCII characters.