Well, I’m two for three, should I apply anyway?

As a front-end developer with 10 years of experience, I’d suggest going with JavaScript. It’s one language for both stacks, you can learn the core front and back end ideologies, and if you decide to go with a different language for back-end, it shouldn’t take too much time to learn afterwards. From my experience it would be easier both to learn and potentially to get a job in the field.