Many filesystems don't support unicode or support only a subset of it:
> Also domains and URLs can be unicode too.
Domains: it depends at which level you are dealing with them. See https://en.wikipedia.org/wiki/Internationalized_domain_name
Internationalized domain names are stored in the Domain
Name System as ASCII strings using Punycode transcription.
only alphanumerics, the special characters "$-_.+!*'(),", and
reserved characters used for their reserved purposes may be used
unencoded within a URL.