It is possible to neither to "undo" (like Ctrl+Z) nor to "find" (like Ctrl+F) in the WM application. It is possible only to "select all" (like Ctrl+A), to "copy" (like Ctrl+C) and to "paste" (like Ctrl+V).
WM 2.0.102 from 14th May2015 (and Beta WM 2.0.103 from 11th June 2015) but these issues have already been around for some time.
Samsung Galaxy S4, 5', 2GB RAM, Android 5.0.1
Reported by B.mertlik on cswiki (item 5). He has said he doesn't speak English good enough to report his issues with Wikipedia Mobile himself.