I know nobody cares if you can write "hello, world" in many languages, but I never stated that or anything like that, did I?
Some things take time to learn (systems programming, memory management, ... are things you'll have to wrap your head around when coming from a higher level environment, for instance), but hardly any of them are language specific as far as I can tell. Feel free to point out examples to the contrary, although I feel like if it's hard to learn a general concept in a specific language, that sounds like a language design problem.
In many cases being a good programmer in one language means you can learn another language and become a proficient or good programmer in it relatively easily. Some specialization is fine, however, if you really stick to a single language/framework/environment, I think you're staking an awful lot on something that could mostly go away in five years time.
For example, I work in the embedded domain. Ten, fifteen years back, microcontrollers were pretty much king. You wrote software close to the metal, without an operating system, and allocated all memory statically. If you stuck to that kind of development, and refused to learn embedded Linux stuff or dynamic memory management, you'd be unable to find a job today (at least in my area, I can't speak for the entire world in this case.)