The cognate phrase in Spanish is El hombre propone, Dios dispone (y el Diablo descompone); disponer in Spanish means something like "to be willing" and also "to have available" and descomponer is "to take apart" or "to disassemble" so I've always interpreted it as "Man plans, God makes it possible, but the Devil undoes things." Which, obviously, would be the opposite of God's role in the English phrase.
Last night I was reading a book my mother-in-law sent me that was set in Italy and one character kept quoting Italian phrases, and one of the ones he quoted was a cognate of the English and Spanish phrases that I, unfortunately, can't find right now, so pardon my Italian: L'uomo propone ma Dio dispone. And in the context in which it was used, it seemed to mean something more like the English phrase: "You made plans, but God will see to it that they work out differently."
2. Am I misunderstanding the meaning of one or more of those phrases (English/Spanish/Italian)?
3. Does the Italian phrase really mean the same as the English one?
4. What other languages have sayings using the same turn of phrase (I assume French does, for example), and what do those phrases mean/in what context are they used in those languages?