It is very annoying to me to hear Erlang referenced as a "pet language". It has been around as a language for 28 years, and it has been doing mission critical, soft realtime work of routing billions of phone calls a day for over 20. It wasn't some academic language with no industry chops.

Using it to dependably route billions of messages a day is not some crazy off the wall "adopting a pet language" -- it was picking a language that had already been proven (and explicitly designed) to work in a very similar problem domain. It was a smart, reasonable, sane choice that they then pushed to awesome extremes.