Setting locale

Hi there,
I am trying to set the --locale for a database but receive 'invalid locale
name'

Here is the posgresql.conf part:

lc_messages = 'en_US.UTF-8' # locale for system error message
# strings
lc_monetary = 'en_US.UTF-8' # locale for monetary formatting
lc_numeric = 'en_US.UTF-8' # locale for number formatting
lc_time = 'en_US.UTF-8' # locale for time formatting
default_text_search_config = 'pg_catalog.english'

locale -a says:

C
en_US.utf8
hu_HU.utf8
POSIX

I would like to use hu_HU.utf8:

createdb -E UTF8 --locale='hu_HU.utf8' test
Password:
createdb: database creation failed: ERROR: invalid locale name hu_HU.utf8

Postgresql is on Debian. Default locale is en_US.utf8

Any idea is appreciated.