She's always been Princess Peach in Japan. She was mostly known as "Princess Toadstool" in the US until relatively recently, with a few odd switches here and there. Sometimes she's referred to as "Princess Peach Toadstool" in US games, but I don't think the Toadstool name has made any influence on Japanese products(unlike the US Super Mario Bros. 2, which had a huge influence on the franchise).
Also, Bowser is King Koopa, fun fact. Makes more sense, really, but a bit bland. A few odd name differences litter the Mario franchise. =P