I can't speak for present day, but, while I was still working there a few years ago, they were pushing Golang pretty hard. They weren't being hard-lined, so I'm sure a lot is still done in other languages, but I wouldn't be surprised if Go rivals at least C++ in terms of service count at this point.

They realized C++ sucks for simple services and due to the Oracle litigation they were trying to get away from Java where possible.

Having written backends in C++, Java, Python, Rust, and Golang myself, Golang is far and away the best tool for the job in my opinion.