This app was mentioned in 2 comments, with an average of 1.00 upvote
I use Google Translate with the camera feature for translating text (take a photo and use your finger to highlight, the instant translation is neat but somehow gets much worse results).
As a tourist though, if you need to communicate with a human, I would recommend VoiceTra. Unlike Translate, it specializes in Japanese and it's eerily good, at least when compared to the nonsense that Translate often spits out. It won't be perfect, but for hanging out as a tourist, it'll be fine.
https://play.google.com/store/apps/details?id=jp.go.nict.voicetra This is the best for Japan.