There's a lot of baggage that comes with each language. I could probably learn any language at that point, but it also takes time to learn whole ecosystem, mostly used libraries and tools. You typically can't do this in week or two, because you need to actually write something and see how it feels, if there are any surprises.

You would probably not want someone with little experience in given language, to touch production codebase without review, because there are always traps that you might've not encountered in other languages.

I typically don't touch low-level programming languages, but once I had to use C to write some small adapter to communicate with some Oracle product. I did it, it worked as expected, but I would not be able to use it efficiently for complex solutions without more experience with creating and managing solutions in C.

I can also write in Go with some basic proficiency, I felt confident at one point in my abilities, but when my code got reviewed by someone specialized in Go, he would propose several improvements that did not cross my mind, because I had less experience in Go.