I generally agree with this, there's specific circumstances but for the most part its true.
I went from a C# position to PHP, to Python, to perl all with little or no experience with what I was jumping in to. There's different nuances and the syntax might take a bit to get used to but as long as someone understands the how and why of what their code is doing that can be pretty easily transfer to most other languages. It's all about the fundamentals.
This is a great response that I'm gone a steal the next timee someone has an issue with my son carrying around an Elsa doll