I think Ex-word models with extended English contents should satisfy your criteria. To be specific, XD-SX4910 or XD-SX9800. As of now, the price of the former is around 26,000 JPY and that of the latter 36,000 JPY ('Very good' ones at 20,000 JPY) at amazon. Also the previous generation model XD-SR9800 of the latter costs around 10,000 JPY second hand.
Both contain E-E, E-J, J-E, J-J dictionaries with audio (for both languages). So it should be fine as regards 1,2,5,6 assuming US/UK English should not be an issue for Longman (or Oxford). I don't think I've seen models with American dictionaries.
They also have functionalities for 4 and 9. As for 7 and 9, it should be acceptable (it is durable but about battery I'm less sure). As for 3, I guess it should be straightforward except perhaps how to use flashcards or bookmarks.
- English dictionary data is US English
- Includes audio for English pronunciation (US English)
- Interface is easy and intuitive enough for an 8-year-old kid to use
- Japanese has handwriting input (via
finger or stylus) for kanji lookup
- Includes English word definitions
in English (not only Japanese translations)
- Includes Japanese word
definitions in Japanese (not only English translations)
- Is durable
- Has good battery efficiency (doesn't require
- An "add to favorites" word list (with
flashcard functionality) would be a plus
Assuming you are in Tokyo, I'd recommend you check them in local shops. One thing in particular is handwriting recognition isn't quite good. But I don't think there is any alternative. So if you don't like them, you may want to buy it used (you may need to be a bit careful though). Any Ex-words with 9800 should have similar contents, but SR/SX ones have significantly better screens.