I've gotten some stored procedures to work with LANGUAGE plpgsql, but now I want to start writing stored procedures using LANGUAGE pltcl but I'm having problems setting things up.

I've installed some extra packages (although I'm not sure why the website I was looking at wanted me to also install the package for Perl, but I did it anyway).
sudo apt-get install postgresql-pltcl-15
sudo apt-get install postgresql-plperl-15
sudo apt install postgresql-15-postgis-3-scripts
I've seen in pgAdmin there is something about Languages and the only one there is plpgsql. I don't know what to do about that, I don't know what options to select if I try to add pltcl here, and I haven't seen any websites saying to change this. So I've left this alone.

I've been reading about CREATE EXTENSION pltcl; command and it just doesn't seem to work.
ERROR:  could not open extension control file "/usr/share/postgresql/14/extension/pltcl.control": No such file or directory
I can't find any help about this error message. Any ideas?