Download the complete Wikipedia to read off line or even customize it, with XOWA
XOWA is a free program that lets you save on your PC a full version of Wikipedia, even providing a convenient way to edit and customize it.
The program resembles the original on line site of the famous encyclopedia and it supports not only Wikipedia articles and media files, but also Wikiquote, Wiktionary, and Wikisource — in any language you may need.
A great feature of XOWA is that you can add bookmarks to continue using Wikipedia where you left from. A dedicated editing tab lets you edit articles the way you are familiar with from the on line version.
Of course, as you can guess, you are going to need some time to download all those huge Wiki files. Updates can also be downloaded.