Only Bing Maps for WP7 is updated. WP8 uses HERE Maps data so Japan map is empty.
These are the some apps that I will be using on my Android device:
1. Google Maps and Google Maps Engine for routes with multiple POIs. GMaps is very limited compared to Google Maps which lets you look around for restaurants, etc.
2. Google Translate (Bing Translator doesn't support Japanese)
3. HYPERDIA JapanRailSearch
4. Japan Trains
5. MapsWithMe with full offline Japan map with POIs and search
6. TripAdvisor City Guides Catalog
7. TouristEye - Travel Guide
This made me realize that there's indeed a big app gap. Hopefully Microsoft will do something. I'll still be using my 1520 as my main phone but I'm not sure for how long.