This is a second attempt at:
#33001

We had to [revert the
commit](#33157) because it
was performing a site-setting check at boot time, which is prone to
issues and not allowed.

This PR:
- re-introduces the changes in the original PR
- a fix by not performing a site-setting check at boot time (verified
by: `SKIP_DB_AND_REDIS=1 DISCOURSE_DEV_DB="nonexist" bin/rails runner
"puts 'booted'"` locally and should be caught by the new CI check
introduced here: #33158)
- adds a fix to the translation editor to not show the original post
locale in the dropdown, as well as adding an indicator of what the
original post locale is in a small badge in the header:
- ![Screenshot 2025-06-11 at 08 42
36](https://github.com/user-attachments/assets/5f0944c5-ec4d-40b3-b97f-25b1fcab8329)