After reinstalling on a virtual machine instead of a container, it works. So the problem seems to be there.
I'm not marking this as resolved yet; I'd like to know what's wrong with the container.

Since I'm in the area, I'd like to take this opportunity to thank you for this tool. I hope...

Thank you.

It is indeed a new installation. I had already completed that part, and locales-all is already installed.
I should mention that it's a Proxmox container, in case that makes a difference.

Hello,
Wapt server: 1.8.1
debian buster

A problem with postconf when installing the database


[*] postgresql - creating db wapt
ERROR: new encoding (UTF8) is incompatible with the encoding of the template database (SQL_ASCII)
HINT: Use the same encoding as in the template database, or ...