Note that technically, as a result of our transition to CC-BY-SA, a link to the original article is enough to satisfy the license. However, I agree that, as a courtesy, the Vietnamese Wikipedia should be better about explicitly crediting the source wiki in translations. In the past, I would simply add an interwiki and state Dịch từ Wikipedia tiếng Anh ("Translated from the English Wikipedia") in the first edit's summary. Do you happen to know how other wikis tend to do this, especially wikis with fewer than 100,000 articles (since they primarily translate)? –  (talk, contribs)