Google is so huge now, I'm not sure if that is really something that you can state unequivocally. The search engine and a lot of the plumbing that everything is built on top of is written primarily in C++, but there is a TON of both Java and Python code there (and that's not counting things like Go and specialized languages like the infamous Sawzall).
Back in the day (particularly before they started doing ads), almost everything was C++.
Only tools, one-offs, and small internal products at Google can use Python. In general, for production it is disallowed (with exception of YouTube). They learned with YouTube that Python doesn't scale well to hundreds or thousands of developers. Even Mondrian, the code review system started by Guido and written in python, was replaced by something more scalable.
Yeah, I'd say Java and C++ are about equally prevalent at Google. A lot of the older products and core infra is still C++, and a ton of new stuff is Java (See: Android).
Back in the day (particularly before they started doing ads), almost everything was C++.