My company is an example of this, and in a way that is quite different from that laid out in the article. We actually began with a Python implementation for our integration / API server. But this was well before asyncio and eventlet and kestral. It didn't scale well, and we quickly outgrew it.

We implemented its replacement in Elixir, a solution we are still running. It is written by a developer we still have, is well organized, follows proper functional paradigms, and fully leverages OTP/Genserver. It is resilient, and so far as the one two developers we have working in it at present, easy to maintain. We love it.

But we also are switching back to Python. The reason is simple: We only have two Elixir developers (really only 1.5), and we have far more work than they can complete. And when something breaks (usually because something changed in the various systems being integrated), we have one guy who can fix it, and get our production queues flowing again.

We have looked for more Elixir developers. They are rare beasts. But we have a lot of Python developers. And now that we have asyncio/eventlet/etc., the landscape has drastically changed. In Python, the various teams can create their own worker modules, and do so more efficiently because they know their own workloads far better.

Language diversity IS a problem when it impedes development and puts production at risk.