Python
After learning machine learning with ROOT the next step is to translate this into Python which is a newer language that is said to faster and more efficient. Fortunately, since this language is taking off there is a lot of more information about it online. When looking to specifically learn the machine learning aspect I found this video series very informative.
However, videos can only get you so far. A more hands on learning approach is one I found called kaggle which is website for programmers to upload their code to competitions for machine learning, but they have a very nice learning process too