[stevepeg]

I would say that curiosity about languages in general is one item that you should look for in candidates. Not the only one of course but curious people do tend to learn and adapt well.

For an analogy, I wouldn't hire a pilot that isn't interested in other planes than what's on their license. What if I want to operate some new models?

Unless I'm looking for someone for a truly specialised role, I would avoid people that stick to only one thing for their entire careers.

[ncmncm]

Curiosity is a quality, but not a qualification.

For hiring, what you should look for, first and foremost, is competence. Curiosity is not a substitute.

[nicoburns]

Curiosity is a decent indicator one of the many types of competence that you ought to be assessing: the ability to learn new skills and deal with problems that are outside of their current skill set. Which for most software jobs is rather key skill.