It's difficult to compare the two because they describe different aspects of the product. The English page has testimonials, pricing information, and some miscellaneous FAQ; the Japanese page has comparisons with email and Skype (the FAQ and pricing are on separate pages).

The Japanese page describes the product's features a bit more succinctly, as they forego the tabs (Group Chat/Mobile/Files/Tasks) for a flat layout with a single paragraph describing each.