Shreyansh Paliwal [off-list ref] writes:

quoted

Yeah, that was a bit confusing for me until I got used to it. Maybe
saying “[default: UTF-8]” would be a small and definite improvement?

The current message can be mistaken, if the reader does not READ, if
it is asking a yes/no question, but with the "default" label, you
cannot imagine answering "yes", which is clearly not one of the
things in the same class as "UTF-8" that is given as the default,
which also serves as an example.

This is indeed a clever hack (not hack on computer code but hack on
the mind of human who is reading the message).  

That makes sense, I tried it below.
I also wondered whether, in addition to this, it might be helpful to warn on
an invalid charset, and/or possibly fall back to UTF-8.

Agreed on the first half of the statement, if we have an easy and
portable way to tell if a given random string names a valid charset.
I do not recommend to "fall back" to anything, if we are asking an
input from the user.

Thanks.