What happens:

Installed using latest live PureOS ISO, but users report this for OEM ISO as well.

GNOME settings cannot see any language or formats:

Workaround

After I did:

sudo sh -c 'echo "en_US.UTF-8 UTF-8" >> /etc/locale.gen'
sudo sh -c 'echo "bs_BA.UTF-8 UTF-8" >> /etc/locale.gen'
sudo sh -c 'echo "sr_RS UTF-8" >> /etc/locale.gen'
sudo sh -c 'echo "sr_RS@latin UTF-8" >> /etc/locale.gen'
sudo locale-gen

I was able to select English, Bosnian or Serbian language and/or formats:

What should happen:

The installer should pick this up automatically.
GNOME settings should be able to select any language, regardless of what's un-commented in locale.gen.