As a hiring manager, I now look for at least two languages, and they don't need to be the tech stack we're currently using. If you're a good developer, and you know more than one language, you understand that picking up another is not an insurmountable barrier. You'll pick up our stack soon enough.
What I need to know is if you can think critically, not if you already know what we plan to teach.
Same here. Depending on the team I'm leading, I can actually consider not having the current stack a plus, as an outsider's perspective on architecture can help grow a team and codebase that's been stuck doing things the same way for a long time.
There's some penalty in ramp-up time, but I find it more than pays for itself down the road.
What else do you look for ? I recently spoke to a hiring manager and he told me that my resume made me look very “green”. It’s only after talking to me that he noticed my resume paints a bad picture.
What I need to know is if you can think critically, not if you already know what we plan to teach.