Actually, Luther posted his theses in Latin and didn't originally intend to question Catholic authority. Instead, he wanted to spark a debate about true repentance in light of the trend, at the time, of selling indulgences to save people from spending time in Purgatory. It was only later that Luther did something truly revolutionary - when asked who had the final authority, the Bible or the Pope, Luther answered that it was the Bible. Based on this belief, Luther translated the Bible into German so that lay people, for the first time, could understand and read Scripture for themselves.
We learned all this from our pastor, who dressed as Martin Luther (a monk) for the occasion of our church's Reformation Day party! Also featured were some German foods including sauerkraut, bratwurst, pretzel rolls, and apple cake (and pizza because the Reformation spread to Italy). We played, "nail the 95 theses to the door," aided and abetted by the children in attendance, and attempted to toss coins into a coffer (a play on John Tetzel's saying that, "When a coin in the coffer rings, a soul from purgatory springs") rather unsuccessfully. It was a fun night, learning some history and celebrating God's work in the church!