By the way, I‘ve talked with Amazon Germany (I‘m German) about whether I‘d be able to buy books from the Japanese Kindle store in the near future or not – they told me that amazon.co.jp acts as an individual company and so they cannot give me any information about that.
So, my guess is that amazon japan will never ever open its store for international customers. This makes the Kindle readers a really bad choice for people who want to read japanese content (books/manga).
Any reader which supports japanese text and open formats and different kinds of DRM is a much better choice for japanese books.
And readers with SD slot are much better for sideloaded manga.
I'll be getting Pocketbook Basic reader for free next week. I don't know whether it even supports japanese fonts and it may be to low res for manga. But maybe it's good enough to wait for the next generation of readers - maybe Kobo will offer better dictionaries till then.
And if I don't like the Pocketbook at all, I'll buy a Kobo Glo instead.