bash: non existent locale crashes bash

Imported from Debian bug http://bugs.debian.org/1021109:

Package: libc6
Version: 2.35-1
Severity: grave
Justification: renders package unusable
X-Debbugs-Cc: <email address hidden>

Dear maintainer,

After upgrading to libc6 2.35-1 (or 2.36-1 in experimental), nonexistent locale setting
starts to crash the system.

This is dangerous because a remote system might not always have the same locale installed.
An auto update will soft-brick the system unless the sysadmin knows to set their LC_ALL=POSIX
before attempting to ssh.

Steps to reproduce:

From a clean installed Debian sid, upgrade to libc6 2.35-1.
Only install C locale and en_US.UTF-8.

$ LC_ALL=ja_JP.UTF-8 bash
bash: warning: setlocale: LC_ALL: cannot change locale (ja_JP.UTF-8)
Segmentation fault (core dumped)

$ LC_ALL=ja_JP.UTF-8 gdb bash

Fatal signal: Segmentation fault
----- Backtrace -----
0x55ed3e1e8dcf ???
0x55ed3e2df312 ???
0x55ed3e2df488 ???
0x7f0b4a39ba9f ???
0x7f0b4b412204 _rl_init_locale
0x7f0b4b4122f1 _rl_init_eightbit
0x7f0b4b3f10f2 rl_initialize
... snip ...

Downgrade to 2.34-8 seems also don't fix the issue, probably some locale
state was invalidated when upgrading.

Thanks,
Kan-Ru

-- System Information:
Debian Release: bookworm/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.19.0-2-amd64 (SMP w/8 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libc6 depends on:
ii libgcc-s1 12.2.0-3

Versions of packages libc6 recommends:
ii libidn2-0 2.3.3-1+b1

Versions of packages libc6 suggests:
ii debconf [debconf-2.0] 1.5.79
pn glibc-doc <none>
ii libc-l10n 2.35-1
pn libnss-nis <none>
pn libnss-nisplus <none>
ii locales 2.35-1

-- debconf information:
  glibc/kernel-too-old:
  glibc/restart-failed:
  glibc/disable-screensaver:
  glibc/upgrade: true
* libraries/restart-without-asking: false
* glibc/restart-services: cron
  glibc/kernel-not-supported: