If you already program quite well, then I expect that you will find this software quite easy to learn. Sage, in particular, is built on top of Python.

That doesn't mean the math you implement in this software will be easy! But I expect that the programming itself won't prove to be much of an obstacle.

I definitely recommend you learn one or more of these languages -- but not necessarily to the scale where you're writing large and complicated programs. I use PARI/GP, a software package similar to Sage which is well suited for number theory in particular -- and my particular use case is a 40-to-150 line program that carries out some particular computation I'm interested in. Usually it will just be simple functions, array manipulations, for loops, computations, library calls -- programming at the level you'd master by the end of an intro CS course.