There's a single A4 page reference/overview of docx4j aka a cheat sheet, in PDF or PNG format.
A much longer introductory guide to using docx4j can be found at http://dev.plutext.org/svn/docx4j/trunk/docx4j/docs/, in various formats and languages.
The translations from English were done with Google Translate. If one of these translations proves useful to you, please let us know and blog/twitter/link to it in your own language. Thanks.
If you want to read the Getting Started guide in a different language, you can run
http://dev.plutext.org/svn/docx4j/trunk/docx4j/docs/Docx4j_GettingStarted_foreign.html through Google Translate.