To open ZIM files, Kiwix uses the Android Mediastore. Unfortunately, the Mediastore is not always synchronized with the filesystem. See the bug report at https://sourceforge.net/p/kiwix/bugs/660/. Kiwix is a Wikipedia offline reader. This task is related to the new release of its Android mobile app. Instructions to compile the app can be found here (Android section). This requires knowledge of the Java programming language.