The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/9.6/static/external-pl.html
Description:
This page seems a bit out of date:
https://www.postgresql.org/docs/current/static/external-pl.html
It lists PL/Ruby which is a defunct project. PL/PHP looks like last updated
2001 so may not work with newer PostgreSQL and PHP.
It doesn't list PL/V8 which I think is very popular these days.