unrecognized language 'plpgsql' - Mailing list pgsql-sql

Hi,

when creating a function I get the error message 'unrecognized
language'.
What's this? I need a powerful language which can retrieve many things
(username, tables, attributes, etc.).
Isn't plpgsql the best choice? Why this message and where can I find
more documentation on plpgsql?

Thank you,

Markus