"Completely different" is a difficult concept when comparing languages... Not only because similarity is a gradient, not a category; but also because most major

"Completely different" is a difficult concept when comparing languages... Not only because similarity is a gradient, not a category; but also because most major languages today are in some way or another descended from C. So the answer to your question will probably hinge largely on the degree of similarity between your known languages and the one you wish to learn. To give a personal example: I currently know Java, Python, Common Lisp and R, in the sense that I have written non-trivial code in these. Last year, I tried to teach myself Haskell, and failed miserably. It was a very different syntax to everything else I knew and had several concepts that were quite alien to me. (It didn't help either that I didn't strictly need to learn it, and didn't have much spare time on my hands...) This year I am having to learn Julia for a project I joined, and I am finding it much easier. Although it isn't quite like any of the other languages I know, its syntax is close enough and I am already acquainted with its concepts. The result was that two weeks after my first exposure, I was ready to contribute code.