> Using an environment variable is not the holy grail for this. On
> writing a non-single-user application you can't expect the user to set
> extra environment variables.

I am not understanding why the user would have to set anything at all.
What is the use case for per-user encoding settings?

I understand that passing LANG=C (e.g. to disable a program's
translations) forces ASCII instead of UTF-8, which is a flaw. Perhaps
the filesystem encoding should be set to UTF-8 when the system locale
says ASCII.

(OTOH, it's IMHO a system bug that LANG=C forces the ASCII charset;
we're not in the 80s anymore)