I've had 4 programming jobs in my life, and for 3 of them I had no experience at all with the language before starting the job. The 1 for which I did have experience ended up being a complete disaster of a workplace.
If there's any correlation between how well you know a specific programming language before taking a job, and how you can get/do a job at a place where they use that language, I have yet to see it in my 10+ years. I'd say it's probably one of the least important factors contributing to your success.
Unless you plan to work at a company for a very short period of time, you'll learn many new things, and probably new languages, while working there. Whether you happen to know the one they're using now is like how tall Michael Jordan was when he was in high school: after a few dozen/hundred/thousand hours of practice, completely irrelevant.