I think this all comes down to using the right tool for the right job. I've worked in polyglot environments where the decision to use multiple languages and platforms was a complete disaster. There's just no need to use two tools, which perform the same tasks at the same speed, for one job. It makes hiring a nightmare, and means the team may become conversant in 10 languages, but never master any of them.
That said, sometimes (and I do mean sometimes), there is a justification and reason for this sort of thing. Facebook chat was written in Erlang for speed and scalability purposes. That makes sense. The application needed more than the standard platform (PHP) could handle.
That said, sometimes (and I do mean sometimes), there is a justification and reason for this sort of thing. Facebook chat was written in Erlang for speed and scalability purposes. That makes sense. The application needed more than the standard platform (PHP) could handle.