Google is most definitely not a polyglot programming environment. There are five and a half blessed languages (C++, Java, Python, JS/TypeScript, and Go), and getting a new one added and approved is a major undertaking, and not guaranteed to succeed no matter how much effort you apply. And you'll still need to do your job. Even if your language of choice does get added, that doesn't mean you can use it on your project of choice. You code in what the rest of the code near you is written in. It's a sacrifice, but one I'm personally willing to make.
Can you perhaps talk a little about what your team and the teams around you are working on? What are the problems you are trying to solve? Happy to take this to another forum, if you don't want to talk publicly.
Also, even the PHP/Hack code is way more delightful than any Java codebase I've touched. :P
Tough decision indeed.