You can download a copy of all of Wikipedia and keep it locally. Without images or media files, the full text of English Wikipedia was about 40GB last time I downloaded it. Full French was 32GB with media. There are simplified versions too with just the most popular content that are just a few GB and you can keep them on your phone.

Edit: http://xowa.org/ is how you do it. Don't worry about server load; these download repositories are from mirrors and torrents so they don't load Wikipedia's main servers at all.