The SDK components can be utilized at two levels:
User Interface: the classes in the package com.xmlmind.spellcheck.ui form a Swing User Interface built above the core Spell Checker engine. This package is the one to be used in most applications.
A very easy integration can be achieved by using a few static methods in the class JSpellDialog.
Core Engine: meant for advanced usage, or for batch-style applications where no User Interface is needed. The package is com.xmlmind.spellcheck.engine.
In the documentation and in the API, the word "language" is often used in place of "dictionary": this is because there is generally one dictionary per language, and the short language name (for example "en") can be used instead of the longer name "en/default". But it is possible for a language to have several different dictionaries.