"What is climbing up onto the walls?"
Translation:Mi mászik a falakra?
Almost, or actually, the same sentence suggests onto and accepted on, and here it even suggests up onto, which makes the two sentences just even more different.
up onto says to me that the onto movement is happening from below. But onto can happen from up onto, down onto, sideways onto. I don't know. The Hungarian sentence just says onto. From somewhere.
My English is certainly not perfect, but those translations appear shaky and too often misleading.