I think it would be great to have the possibility to make a feedback about a wrong translation, to help a better translation in the future. I saw many wrong translations in translations of English pages in French.. So if I could help..
We have started working on this feature. We are planning to give users the possibility to rate translations as good or bad, and, in case of bad, choose the reason why.
For example, if a Traditional Chinese native speaker (like me) using Firefox Nightly to test the unstable English => Traditional Chinese translation model under development (if it exists), and finds an error in the translated page, they have to find the link to the form, open the link, and fill out the feedback. It is not as convenient as clicking on the feedback option on the translated page and then filling out the feedback.
P.S. I didn't fill out this form, because there is no translation model in Traditional Chinese.