I like the way the translations are at a sentence-by-sentence level. I think it makes you more of a language learning tool, rather than a social translation site like Yeeyan where the major goal is just making a translation of the whole article.

Being able to show the whole translation history of a sentence as soon as you click on it is also a good idea (is that what you're doing? I didn't notice any sentences with more than one previous translation, so I can't confirm it).

Here are some changes I would make if it was my site (just some ideas, they might not be particularly good):

* A bilingual/comparison mode, like Yeeyan's 左右对照 view, so you can see both the original and the translated articles at the same time

* Default to the latest translation when you click 'translate' on a sentence that's already been translated, instead of a blank textbox (I think most changes will be relatively minor corrections rather than re-translating the sentence from scratch)

* Continue to show the edit history of a sentence even when you've clicked 'translate'; also have a way to copy an old translation to the translation textbox for editing (just click on it?)

* Edit summaries for translations (optional, of course), so you can see why the translator thinks the new translation is an improvement over the old one

Also, I haven't really studied Japanese much so I might be wrong about this, but might it be better to show the kana as ruby instead of as a big long string below the sentence? That way it's easier to know what pronunciation maps to what word. Or perhaps highlight the appropriate kana when you mouseover a word. And is it normal to convert katakana to hiragana in that section, that seems a bit weird to me.

I created an account, but my Japanese isn't good enough to take part in this sort of project. I'll definitely be interested when you launch the Chinese version.