I found this thread by accident and I couldn't help but be interested in it. I'm half-japanese so I hope my opinion might be a little helpful. ^^
I totally agree with you about the language benefit. If you want to work in Asia, maybe J-school is a wise choice since many big companies operating in the region are undoubtedly Japanese! And by learning Japanese, it's very easy that you will get to learn Chinese, too (by Kanji).
As for Nagoya's MBA, the program is internationally accredited, but I don't really know much about it since I'm not a permanent resident in Japan. But the university itself is really famous (one of national seven universities - kinda like ivy leagues). It's a prestige one. So, I think it's a really good choice. But there are other schools in Tokyo that might be more famous nationally. Well, here are my personal Top 3 based on academic excellences and international reputation..
1. Keio University - Very reputable. The program is accredited by AACSB, so, no worry. One-third of the cases taught here also comes from HBS.
2. Waseda University - Another reputable one, but a little lost to Keio. However, the faculty produces the greatest number of CEOs than any other universities. Their alumnus are founders of Honda, Nintendo, Sony, Samsung.. etc. So, great network for sure.
3. Hitotsubashi University - Small and new but cool. Very well-respected in Japan and East Asian.
Anyway, I'm sure that Nagoya won't lose to these schools. It may not be as famous but I believe it's also great. Furthermore, Nagoya is a very nice place to stay, very beautiful. So I suggest you choose the one you want to spend two years of your life time with. Living in Japan itself has many advantages. In my opinion, it's one of very worthy life experience. Wherever you choose to study, I can assure you that knowing Japanese is a big plus in both private and professional life