Create Language Error

Hi!

Im trying to install sql-ledger but I got:
ERROR: language "plpgsql" does not exist
HINT: Use CREATE LANGUAGE to load the language into the database

...then I use CREATE LANGUAGE, but;

postgres=# CREATE LANGUAGE pgpsql
postgres-# ;
ERROR: unsupported language «pgpsql»
HINT: The supported languages are listed in the pg_pltemplate

... don't know what im doing wrong :-S

My system:
Ubuntu 8.04
postgresql 8.3.5
sql-ledger 2.6.22
apache  2.2

Thanks for any hint!