lc_messages on 8.3.7

Hi,

Postgresql 8.2.13 on Windows (it's correct, "Leden" is the Czech translation of "January"):

postgres=# SET lc_messages=en;select to_char('2006/01/01'::timestamp, 'TMMonth');
SET
to_char
---------
January

postgres=# SET lc_messages=cs;select to_char('2006/01/01'::timestamp, 'TMMonth');
SET
to_char
---------
Leden

Postgresql 8.3.7 on Windows (wrong):

postgres=# SET lc_messages=en;select to_char('2006/01/01'::timestamp, 'TMMonth');
SET
to_char
---------
January

postgres=# SET lc_messages=cs;select to_char('2006/01/01'::timestamp, 'TMMonth');
SET
to_char
---------
January

Do you have any idea what happens in 8.3.7?

Thank you.
Pribram