I used to do that a year or two ago and it was pretty straightforward back than (there was «Export to epub» link or something like this on the left pane of a Wikipedia page). Not any more! Currently, there are two options for export in the book creator, namely, «pdf» and «plain text» (only «pdf» for single article).
What is worth I did not manage to find any clear info on why it is not there. The article at https://en.wikipedia.org/wiki/Wikipedia:Tools#PDF.2C_EPub.2C_Odt_and_LaTeX mentions it is still possible to produce epubs and re-directs to some weird page.
Do I miss anything obvious or they really disabled this useful functionality for good?
Best Answer
The wired page was written by me. It links to the following page, where you can put in a link to a wikipedia article and download the corresponding epub file. http://mediawiki2latex.wmflabs.org/ Greetings from the cowshed. Yours Dirk