Andreas Karlsson <andreas(at)proxel(dot)se> writes:
> Hm, I like the idea but I see some issues.
> Enforcing the BCP47 seems like a good thing to me. I do not see any
> reason to allow input with syntax errors. The issue though is that we do
> not want to break people's databases when they upgrade to PostgreSQL 11.
> What if they have specified the locale in the old non-ICU format or they
> have a bogus value and we then error out on pg_upgrade or pg_restore?
Well, if PG10 shipped with that restriction in place then it wouldn't
be an issue ;-)
regards, tom lane