Good question :) SRE-written system are never or almost never written in Java. However many SRE teams support Java systems.

Literally nothing at Google except third-party code (like Linux kernel) is written in straight C. C++ is very common, though.

Python sucks and is useless. Most things that were written in python are now written with Go.

I guess your question is about what happens if a C++ expert ends up on a Java team, but I don't really know. I happen to have landed in C++ world, which suited me.