Coming onto a project that already exists is a lot different than selecting a language for whatever new ยต-service is needed today. Nobody wants you to rewrite the code that is already there, but I have seen inside a large number of tech companies, and can tell you that, in 'big tech', language choice for a new project being dictated from up on high would be the exception, not the rule.
Even in stodgier industries that have traditionally been more command-and-control like financial services, we see a LOT more flexibility on platform choices in general, as many organizations are realizing that, if engineers don't get to use the tech they're interested in using, they're becoming more and more likely to look for the door. Everybody good wants to stay relevant and to learn stuff they find interesting.
