Maybe I should've qualified that better. Languages can be interchangeable in purpose, but not in process. By that I mean that sure, I can write a web backend in

Maybe I should've qualified that better. Languages can be interchangeable in purpose, but not in process. By that I mean that sure, I can write a web backend in pretty much any language I choose, but the quality of that backend code and the rapidity with which I can deliver it will heavily correlate with the amount of experience I have with the language in question.