Is it possible to use Stanford Parser in NLTK? (I am not talking about Stanford POS.)
A new development of the Stanford parser based on a neural model, trained using Tensorflow is very recently made available to be used as a python API. This model is supposed to be far more accurate than the Java-based moel. You can certainly integrate with an NLTK pipeline.
Link to the parser. Ther repository contains pre-trained parser models for 53 languages.