In MLA format, to cite a book that has an original author and was later edited and translated by someone else use the following format:
First write the author's name, (here the last name is written first followed by the first name and separated by a comma), then the title of the book(underline the title), the name of the translator and editor, before the names use the notation Trans. and ed., then the place where the book was published, publisher's name and the year in which it was published.
From the details you have provided, we can have:
Ziyang, Zhao. Prisoner of State: The Secret Journal of Premier Zhao Ziyang. Trans. and ed. Bao Pu, Renee Chiang, and Adi Ignatius, "place": "publisher", "year".