Its not the language, its the libraries, the conventions, the external resources. I picked up Ruby and Python, Node and even dusted off my PHP chops to write some modules for a client a few months ago. It wasn't hard, but I spent 20% of my time on the language, 50% figuring out what libraries to use, and another 30% making damn sure that my novice attempts were at least idiomatic and didn't come across as novice (including having them vetted by more seasoned users).
Anyone can write a for() loop in anything. Knowing the massive standard libraries for a language well enough to leverage them (for example, in Java I still see people dragging in external Base64 implementations that haven't been needed in a decade but once were) takes far, far longer.
I want people to write clean code that will be well understood and maintainable by others 5 years from now, not someone who just figures out how to get code to compile.