Translate function and strange results ...

Hi,

Can someone can explain me why it's run like this with PostgreSQL v8.3.8 ?

base=# select translate('Hervé', 'é', 'e');
 translate
-----------
 Herve
(1 row)

base=# select translate('Hervé', 'âàäéèêëïöôùüû', 'aaaeeeeioouuu');
 translate
-----------
 Hervai
(1 row)

base=# \encoding
SQL_ASCII

Thanks,
--
Hervé Piedvache