My example, "OCaml", is not a "language of the month." Its roots are >30 years old and wasn't developed by someone in their basement over the weekend. As stated, Facebook even uses OCaml, among other languages, for good reason.
You try hiring and/or retraining enough engineers to be able to make a switch to OCaml, and see how much it'll cost you.
I detest PHP, but I've still more than once made the choice to do apps in PHP motivated by developer availability alone.
It's not a great language, but with some discipline it is also not nearly as awful as some people like to think, and you can make up for a lot of awful with the difference in ability to hire experienced engineers who know PHP vs. many of the less common languages.
