plr

I am trying to use the PL/R procedural language in a PostgreSQL 9.2 database. I have installed the plr language and I am trying to add it to a database. When I run the command CREATE EXTENSION plr; I get the following error: ERROR: language "C" does not exist STATEMENT: CREATE EXTENSION plr; ERROR: language "C" does not exist When I list the available languages in the database with select * from pg_language; I get lanname | lanowner | lanispl | lanpltrusted | lanplcallfoid | laninline | lanvalidator | lanacl ----------+----------+---------+--------------+---------------+-----------+-----------