Hiring any programmer that can't adapt to an unfamiliar new language is a bad idea (TM).
I'm far from a guru, but I've been able to pick up quite a few different languages, frameworks and structures over my tenure. It's the ones that limit themselves to a single language (be it Java or not) for long periods of time that you need to worry about.
These are the programmers that will build a square wheel because that's what the spec told them to build. Employ them at your peril.
That's cool, but when I'm hiring a team and paying their salaries with my own money, I'm just not going to bank on transitioning anyone from X to Y. No time for it, no appetite for the risk. But if you raise VC, more power to you.
I'm far from a guru, but I've been able to pick up quite a few different languages, frameworks and structures over my tenure. It's the ones that limit themselves to a single language (be it Java or not) for long periods of time that you need to worry about.
These are the programmers that will build a square wheel because that's what the spec told them to build. Employ them at your peril.