(Adds details, quotes and background) LOS ANGELES, Feb 24 (Reuters) - Christoph Waltz on Sunday won his second Oscar for Best Supporting Actor in four years under the direction of Quentin Tarantino, this time as a German bounty hunter in the slave revenge tale "Django Unchained." "We participated in a hero's journey, the hero here being Quentin," a choked up Waltz said as he accepted his award.