Citation, Documentation of Sources

Q. If I am writing out foreign book titles followed by the English title in parentheses, should the English titles appear in italics or quotations?

A. Chicago style writes the translation in plain text, no italics or quotes, no headline caps. Please see CMOS 14.99:

Koniec sojuszu trzech cesarzy [The end of the Three Emperors’ League]

If the book was published under an English title, however, then put the English title in italics as you would any other published book:

Furet, François. Le passé d’une illusion. Paris: Éditions Robert Laffont, 1995. Translated by Deborah Furet as The Passing of an Illusion (Chicago: University of Chicago Press, 1999).