Boot method: CD
Image version: debian-11.3.0-amd64-netinst.iso
Date: 2022-07-20

Machine: qemu VM (via libvirt)

I installed Debian, choose "No localization" at the question and
selected GNOME to be installed (or kept it selected). All other setting
were left on the default.

The relevant part of /var/log/installer/syslog is probably this:

+---
| Jul 20 09:38:15 localechooser: info: Language = 'C'
| Jul 20 09:38:15 localechooser: info: line=C;0;;C;en;
| Jul 20 09:38:15 localechooser: info: Set debian-installer/language = 'en'
| Jul 20 09:38:15 localechooser: info: Default locale = 'C'
| Jul 20 09:38:15 localechooser: info: Set debian-installer/consoledisplay = ''
| Jul 20 09:38:15 debconf: Setting debconf/language to en
| Jul 20 09:38:15 gtk-set-font: Switching to font 'DejaVu Sans' for 'en'
| Jul 20 09:38:21 localechooser: info: Set debian-installer/country = 'DE'
| Jul 20 09:38:21 localechooser: info: Set debian-installer/locale = 'C'
| Jul 20 09:38:21 localechooser: info: System locale (debian-installer/locale) = 'C'
+---

In the installed system, I can't do much as gnome-terminal does not
start. It just shows the app-is-starting animation and then stops. In
the journal I find error messages like:

+---
| Jul 20 11:58:53 [...] systemd[990]: Created slice app-org.gnome.Terminal.slice.
| Jul 20 11:58:53 [...] systemd[990]: Starting GNOME Terminal Server...
| Jul 20 11:58:53 [...] gnome-terminal-server[1915]: Non UTF-8 locale (ANSI_X3.4-1968) is not supported!
| Jul 20 11:58:53 [...] systemd[990]: gnome-terminal-server.service: Main process exited, code=exited, status=8/n/a
| Jul 20 11:58:53 [...] systemd[990]: gnome-terminal-server.service: Failed with result 'exit-code'.
| Jul 20 11:58:53 [...] systemd[990]: Failed to start GNOME Terminal Server.
+---

Running `localectl set-locale C.UTF-8` as root made the system work.

It would be good if choosing "No localization" would use "C.UTF-8"
instead of "C" or there was at least an option for "C-UTF-8". I think I
tried setting "C.UTF-8" via preseeding recently and that was rejected
as an invalid choice (not 100% sure).

Ansgar

Confirmed while testing Debian 12 bookworm installers alpha 1 & 2.
Picking locale "C" when installing desktop causes broken system with GNOME.
A serious issue, as mentioned above, is that gnome-terminal cannot run.
And, no error messages appear to inform user of problem.
journalctl shows:

gnome-terminal-server[2043]: Non UTF-8 locale (ANSI_X3.4-1968) is not supported!

Would help if installer allowed picking locale "C.UTF-8" instead of "C".

However, another GNOME issue arises with locales "C" and "C.UTF-8":

gnome-initial-setup-first-login.service fails with:
ERROR:../gnome-initial-setup/cc-common-language.c:102:cc_common_language_get_current_language: assertion failed: (current_language != NULL)

Ref. upstream GNOME issue "Aborts on startup with LANG=C.UTF-8":
https://gitlab.gnome.org/GNOME/gnome-initial-setup/-/issues/159