Hello,
I've just released a dictionary app for iOS based on Wiktionary data [1] [2].
It works offline, it's free (as in beer), doesn't have ads and integrates with the iOS Wikipedia app. However it's not open source, although that is something I'm considering for later. I haven't had much feedback so far so I'm really curious if you find it useful in its current stage. The main intention is to turn it into a tool for language learning, but it's not quite there yet. It should already be useful as a general purpose offline dictionary though.
Jan
[1] https://en.wiktionary.org/wiki/Wiktionary:Beer_parlour/2017/July#mot.C3.AE.2... [2] https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=104612282...