Mathematica has not only convenient built-in multilingual dictionaries, but also built-in information on word meaning, structure, and usage, as well as the relationship between words. Together with Mathematica's tightly integrated string manipulation functions, visualization, and data import and export, this provides a uniquely powerful platform for natural language computing.
DictionaryLookup — look up words in English and other dictionaries using string patterns
WordData — properties of words and networks of relationships between them
Import — import or "scrape" text from all standard formats
ExampleData — access to standard sample texts, including complete books