The Canon Wordtank IDX-9700 electronic dictionary does everything the smaller IDC-310 does, and more. Of course, you can translate English to Japanese and vice versa. You can also look up kanji based on reading, radical or stroke count, and look up words based on any component kanji.
The most useful function is that you can highlight any displayed word or compound and look it up instantly. This feature alone means it’s worth buying in addition to the IDC-310, though it’s bulkier and twice the price at 10,000 yen. If you ask, you can at least get an English manual.
I haven’t seen this around in shops for a while now. There may be newer models out.