Even simple requirements can rule out languages for me. Like, if you need async or concurrency, Python is awful. If you need SQL in your code, Golang isn't great. If you are building a simple CRUD backend, Java is waste of time. If you aren't doing anything compute heavy or embedded, why even consider C++ or Rust. The list goes on.
But in reality it rarely matters. If you were only allowed to use Java as a backend and your competitors could use anything your company would succeed or fail based on marketing and sales. The backend doesn't matter as long as they both have the same features.
I understand developer preference and different languages make things easier and make programming funnier. Languages have different limits.
As you become more senior you realize getting around those limits is part of the magic. If you come on to a project where the existing developer wants to write the backend in javascript because that's what they know I would rather use Javascript then wasting time trying to push a more 'pure' choice. Because in the end I am capable of writing it and what we will be judged on is if it works to achieve an objective not if it was the best language choice when using differentiation.
If speed of execution matters, then the language and tools you use for something also matters.
I might personally love to kick off a greenfield project with Elixir, and it might tick all the technical boxes and meet the requirements. But then I have to pay a premium for senior engineers that know elixir or have to price in the time needed to upskill.
Or I could just do it in Rails where I can dip into a much larger talent pool and still meet the requirements. Much more boring but can get the job done just as well.
