The main difference is the price , and what you're paying for is kanji-awareness, so you can use maps with Japanese labels.
Edge 530 comes with a map of the region where you buy it, built-in. The built-in map with 530J will be of Japan, and will be in Japanese. if you don't read Japanese well you'll probably want to download an English map set.
The new Garmin Edges look like very capable units. I use an Edge 1000 and am envious of the (claimed) 20 h battery life in Edge 530.
I have the 830J and the UI and all functionality works 100% in English. If you are planning on using the device primarily in Japan I would recommend getting the local version. The one thing to be aware of is that Garmin uses different Firmwares for their devices depending on region, and the ASIAN versions of 830 and 530 are far behind in terms of updates. They should catch up at some point though...