If you want to be a generalist, you may want to learn things which are useful independently of the programming language.
Some books that would qualify in my opinion (as examples):
- Code Complete: A Practical Handbook of Software Construction, Second Edition by Steve McConnell
https://www.amazon.com/Code-Complete-Practical-Handbook-Cons...
- Facts and Fallacies of Software Engineering by Robert L. Glass
https://www.amazon.com/Facts-Fallacies-Software-Engineering-...
Learning the different approches taken by multiple programming languages is certainly useful. It may not be that much relevant which language it is unless you want a job specifically in that language.
I can't speak for Google but I guess it is more relevant how familiar you are with software development practices and general knowledge about architecture, design, testing, algorithms to name a few than a specific language.
[1] https://www.amazon.com/Facts-Fallacies-Software-Engineering-...