It’s very rare in the industry for you to start something and have the flexibility to pick the language. You’re much more likely to be working on an existing system or expected to work with whatever the company uses.
That said, there’s plenty of opportunity to make your own decisions. Having to follow arbitrary style rules is hardly a consideration (actually you’ll find it’s hard enough just to have consistent arbitrary rules within a company).
There may also be opportunities for you to change these rules, but it’s also wise to pick your battles.
Big companies do this all the time. Giant monorepos with good testing and reliability systems manage it. As an example: https://abseil.io/resources/swe-book/html/ch22.html