This app was mentioned in 1 comment, with an average of 1.00 upvote
This Japanese (to Japanese) dictionary https://play.google.com/store/apps/details?id=jp.co.kgc.android.oneswingviewer.WSANN006G
Can't see the price but it was around 13 euros. Kinda slow, and in the end does nothing I couldn't do online. This however works offline. I also have an electronic dictionary (those things that look like Nintendo Ds) and it's much better. Still decided to keep this app because sometimes I really need it.
The best Japanese-English dictionary app is this https://play.google.com/store/apps/details?id=sk.baka.aedict3
Aedict 3. I've tried almost every one of those Japanese dictionary apps and none come even close to Aedict 3. I've bought all the apps from the developer who is super cool and always replies to requests and bug reports. Combined with the Aedict popup reader is perfection for someone who uses Japanese everyday.