Okawix is a free offline reader that allows users to download the content of Wikimedia projects, with or without pictures, in order to then access it offline. If you like Wikimedia projects you should have this reader because you can check any Wiki items without internet access.
First of all, you have to download Okawix. It is not contain Wikimedia projects, after you installed and open it, you can choose any language, project like Wikipedia, Wikisource, Wiktionary, Wikiquote, Wikibooks.
Next step, download your favorite subject. For example, Wikipedia English version is about 11.7GB, click "Download" button, it will download file automatically. You can choose multiple languages, different versions have different sizes.
Last step is open Wiki project, just click item on left side after search keywords. Pretty easy.