Even when I was back in college many years ago, only the first class taught a language. From that point forward the teacher of each class said we're using language X and suggested a book if you needed help learning.
Sure, it's true that many things about good design are language agnostic. On the other hand, frameworks and languages can actually limit or enable what you can do, and that lack of familiarity with them has the potential to lead to mistakes.
My reasoning for this is that we are always learning new languages and using new frameworks. Why would I let a better person go when the language is probably going to change, or worst case they pick it up in a couple weeks just by looking at the existing code base? One case where I would deviate a bit is if I was hiring for a functional programming position. In that case I would prefer experience with some functional language, but that is not much different than wanting OO experience for a Java/C# position.
You know gazillions of frameworks to achieve everything these days, their integration tricks, various app servers, CI toolsets and so on and on?
I mean, if you are senior in something, are you senior also in XXX language, meaning I give you spec, we talk and you deliver proper maintenable solution, leading dev team, managing all issues and bumps along the road? If no, and you just come as described junior, nobody has time to babysit you for weeks/months, and you are not willing to take junior salary. but that's what you are to the company.