PL/Perl is not installed by default if you used the standard source distribution to install PostgreSQL. If you compile PostgreSQL from the source, you need to configure the script with the --with-perl option.

If you used a binary distribution on your platform, you can normally install PL/Perl using your package manager. You can search for postgresql-plperl, or a similar package name, as it differs across the distributions. Once PostgreSQL is compiled with the correct option, or you have installed the appropriate package, you can create the PL language using the createlang utility or the CREATE LANGUAGE command, as shown here:

$ createlang plperl template1

Or the untrusted version, such as the following command:

$ createlang plperlu template1
hon