From the DuckDuckGo Goodie FAQ:

What if I don't know Perl?

If you don't know Perl, that's OK! Some instant answer types (Fathead, Longtail) don't require the use of Perl. Also, if you know PHP, Ruby, or Python you should be able to write a Goodie in Perl pretty easily using this awesome cheat sheet.

ref: https://duck.co/duckduckhack/faq#goodie

So DDG Goodie plugins can only be written in Perl.

Goodies on the goodies page represent all of the available instant answer types (async API calls, functions, DB full text, and DB keyword).