To test the version of nltk and scikit_learn, you can write a python script and run it. In my opinion it's better to start learning python. I found it easier to learn then c or c++.
Is it okay to first learn python in preparation? With that said, i want to. The r^2 in scikit learn is essentially the same as what is described in the wikipedia article on the coefficient of determination (grep for the most general definition).
Learning python first is ok. Many of the tricks you know that make sense in. So you can use/learn python with access to the.net class library. It will not hinder your experience with gdscript.
It has libraries to do virtually anything you might need, and can do essentially anything. A good place to start is by downloading ironpython and looking at ironpython in action, which is a very good. You will write better python code if you learn to use python idiomatically, than if you try to write python like a c programmer. 219 import nltk is python syntax, and as such won't work in a shell script.