Comment 16 for bug 1134036

imo, this is either a bug in postgres because it fails to install when locale is set to invalid, or its user error.
I'm not sure if whether or not it will become more or less common.

More generally, there is a question of:
 is installing packages on ubuntu with an invalid locale a supported operation?

If so, then postgres has a bug (as do some other packages).

If not, then I'm not really sure what to do.

Martin Pitt (postgres maintainer for ubuntu) clearly stated it is not when closing bug 969462 as 'Invalid'