bin/58609: sh(1) ignores interactive locale changes

[campbell+netbsd%mumble.net@localhost]

>Number:         58609
>Category:       bin
>Synopsis:       sh(1) ignores interactive locale changes
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Aug 16 17:30:01 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 10, 9
>Organization:
The NétBSD Foundation
>Environment:
>Description:
If you start sh(1) with LC_CTYPE=C.UTF-8, you can enter UTF-8 input and sh(1) will consume it.

If you start sh(1) with LC_CTYPE=C, when you enter UTF-8 input, sh(1) will ignore it, as one might expect.

But if you start sh(1) with LC_CTYPE=C, and you do `export LC_CTYPE=C.UTF-8', then when when you enter UTF-8 input, sh(1) will still ignore it.
>How-To-Repeat:
$ LC_CTYPE=C.UTF-8 PS1='(C.UTF-8)$ ' sh
(C.UTF-8)$ echo £
£
(C.UTF-8)$ ^D
$ LC_CTYPE=C PS1='(C)$ ' sh
(C)$ echo                       # type £ -- nothing happens (expected)
(C)$ export LC_CTYPE=C.UTF-8
(C)$ locale
LANG=""
LC_CTYPE="C.UTF-8"
LC_COLLATE="C"
LC_TIME="C"
LC_NUMERIC="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_ALL=""
(C)$ echo                       # type £ -- still nothing happens
>Fix:
Yes, please!