Why we chose Erlang over Python, Ruby, PHP family for our back-end.
The short answer :
Because it’s a completely different approach from the OO programming languages (even from the pure functional ones like Lisp or Haskell), it’s concurrent, stateless, has been battle tested in real large-scale industrial products, has an active web app centric community and finally, because it fits perfectly with our view of a light back-end delivery service engine.