Father Joseph Fessio, S.J. cuts to the heart of the issue, with my emphases:
It is important to note that there are two very serious mistranslations in the Italian version of the Pope’s remarks, upon which many early reports were based, since the embargo was broken by the Vatican newspaper, L’Osservatore Romano. (That’s another story.) First, the German speak of “ein Prostituierter”, which can only be a male prostitute. The normal German word for prostitute is “ [eine] Prostituierte”, which is feminine and refers only to a woman. The Italian translation “una prostituta” simply reverses what the Pope says.Read his whole commentary here.
Equally problematically, “giustificati” = justified, was used in the Italian translation of “begründete”, and arbitrarily resolves the ambiguity one-sidedly.
The Pope responded: “She [the Church] does not regard it as a real or moral solution, but, in this or that case, there can be nonetheless in the intention of reducing the risk of infection, a first step in a movement toward a different way, a more human way, of living sexuality” (italics mine).
In the first place a solution which is not “moral” cannot be “justified”. That is a contradiction and would mean that something in itself morally evil could be “justified” to achieve a good end. Note: the concept of the “lesser evil” is inapplicable here. One may tolerate a lesser evil; one cannot do something which is a lesser evil.
But the crucial distinction here is between the “intention” of the male prostitute, viz. avoiding infecting his client, and the act itself, viz. using a condom. Since this distinction has been missed in almost every report I’ve read, it calls for some elaboration.
This distinction, in moral philosophy, is between the object of an act and the intent of an act. If a man steals in order to fornicate, the intent is to fornicate but the object is the act of theft. There is no necessary connection between stealing and fornicating.
In the case of the Pope’s remark, the intent is preventing infection and the object is use of a condom.