I've seen quite a few environments, and usually there's only a limited current set of tech the devs are allowed to use, and if that's not the case, I try to enforce this, but this set should evolve depending on the needs.

The main issue however is manpower. At my current client, one of the technologies still actively being used for this reason is PHP (which is a horrible fit for microservices for a lot of reasons), because they have a ton of PHP devs employed, and finding a ton of (good) people with something more fitting like Go or Rust knowledge is hard and risky and training costs a lot of money (and more importantly: time)...

At a previous job we used Python for all microservices, except for 'legacy' systems which were in Groovy / Rails. That was a context switch if I ever experienced one.

How is a serde IDL relevant to microservices? XDR would do just as well, so would JSON.