Knowing Python is by no means an absolute prerequisite. Although all of the examples are explicitly illustrated in Python code, we took great pains to try an explain the concepts in general terms first.
I won't say Python is the definitive tool for NLP, but it certainly has one of the richest eco-systems for NLP tools. NLTK, spaCy, to name just two.
The sections on deep-learning for NLP are also exampled in Python, with higher order concepts approached in general terms. However, all of the major deep-learning libraries express apis at the very least in Python. So to really get your feet wet with neural networks, Python will be huge help.
All of that being said. Python is incredibly readable, even to the point of being confused with pseudo-code on occasion. So don't let that be a barrier to entry.