That's actually far more true with computer languages than spoken languages. When a person knows a single programming language, the time it takes to learn a usable subset of any other programming language decreases by probably at least 80%
Most every computer language has the same base elements. Functions, loops, variables, arrays... Though there are still a few more unique features that not every language has, such as objects (with inheritance), pointers, garbage collection, or reference counting.
The hardest part of learning another language will always be Other People's Code. Libraries suck balls. Libraries are the worst. Imagine learning how to speak Spanish, but everyone in Mexico looks at you like you're non-fluent if you can't quote two decades worth of spanish soap-operas.