> There is validity in saying that 'LANG=utf-8' is an invalid setting
Agreed. But that doesn't really explain why e.g. LANG=en_US also
produces "", while LANG=invalid produces "US-ASCII".
> I do wonder how the user ended up with LANG=utf-8 in the first place.
Me too. As far as I can gather, it's a result of setting the Terminal
preferences (particularly the character encoding and 'Set LANG
environment variable on startup' checkbox) in some particular way, on
some versions of OS X, for users in some countries, at some particular
phases of the moon, etc...