Check if language is installed

["Andrus" <kobruleht2@xxxxxx>]

My script running as superuser needs to install plpgsql using

CREATE LANGUAGE plpgsql;


in 8.2+

Which is the best way to check that this command does not cause error ?

Is it best to use 

select true from pg_language where lanname='plpgsql'

for checking for plpgsql existance  before running CREATE LANGUAGE ?

Andrus.