Selected literature:

• David Jurafsky, James Martin: "Speech and Language Processing".
  Source: see https://web.stanford.edu/~jurafsky/slp3/
• The Natural language Toolkit. Source: http://www.nltk.org/
• J. Allen: Natural Language Understanding (Pearson)
•  C. Manning, H. Schütze: Foundations of Statistical Natural Language Processing (MIT Press)
•  S. Russel, P. Norvig: Artificial Intelligence, A Modern Approach (Pearson)