For almost all of the BSDs, Linux distros, Solaris, AIX, HPUX, countless others, you’re going to have both bash and Perl interpreters included by default.

I think installing python is generally quite reasonable! It’s just not as ubiquitous, so if you’re looking for a one-stop interpreted language that most people will neither need to install or worry about the interpreter version, then a baseline old version of bash or Perl is a pretty good bet.

Although really awk probably also deserves consideration in this regard, given that you will even have it on embedded Linux where bash and Perl are not. I don’t know enough about awk to comment on its general utility for doing something like neofetch, however.