Open source Python modules, linguistic data and documentation for
research and development in natural language processing, supporting
dozens of NLP tasks, with distributions for Windows, Mac OSX and
Linux.

NLTK comes with many corpora, toy grammars, trained models, etc. A
complete list is posted at: http://nltk.org/nltk_data/. To retrieve
all the data, use "python3 -m nltk.downloader all". To ensure system
wideinstallation, you can run the command "python3 -m nltk.downloader
-d /usr/share/nltk_data all" as root. Note that the 'regex' package,
also available on SBo, is required to run this command.