For some reason I cannot change the language of the error messages from PostgreSQL. I have tried to set the language inside the script for creating the schema in at the first li
if you have permission for access to $datadir\postgresql.conf, you change lc_messages parameter to 'English_United States.1252'.
After you must reload configuration.
My config settings is here;
#These settings are initialized by initdb, but they can be changed.
lc_messages = 'English_United States.1252' # locale for system error message strings
lc_monetary = 'English_United States.1252' # locale for monetary formatting
lc_numeric = 'English_United States.1252' # locale for number formatting
lc_time = 'English_United States.1252' # locale for time formatting
# default configuration for text search
default_text_search_config = 'pg_catalog.english'
Have you tried the following command?
initdb --locale=en_US --lc_messages=en_US
for details, please refer to http://www.postgresql.org/docs/9.0/static/locale.html