Ugh, you haven't experience pain until you've worked on a project which has a bunch of different languages because Johnny wanted to use Scala, Freddy loved PERL and Sally was learning Elixir on the side. They all left and the new team has to figure out how all these stupid languages even build.
I didn't say "let everyone go off and learn a different language and develop new code in it," obviously that is ridiculous, and would get out of control as you said.
What I did say was there's a working piece of code out there that someone else has already spent time getting to work, but we can't use it because of the language it's written in. For example, I've had problems getting people to use Jenkins because it's written in java. Not that they were trying to write plugins or do anything internal to Jenkins, they just didn't like it because the language it was written in.
