I have to disagree. I’ve been conducting interviews for a fairly large software shop (~2000 engineers) for about 3 years now and, unless I’m doing an intern or very entry level interview, I don’t care what language they use (both personally and from a company interviewer policy), as long as they can show me they understand the principles behind the interview question (usually the design of a small file system or web app)

Most devs with a good understanding of underlying principles will be able to start working on meaningful tasks in a number of days.

It’s the candidates who spent their time deep diving into a specific tool or framework (like leaving a rails/react boot camp or something) that have the hardest time adjusting to new tools.

Plus when your language/framework falls out of favor, you’re left without much recourse.