Answer:
Luther wrote in German. In fact, he was the first to translate the Bible into German and is credited to be one of the fathers of the modern German language.
Explanation:
Luther's booklet being written in German. It was very short and easy for people to understand. Luther's first widely successful work, it was reprinted twenty times. Tetzel responded with a point-by-point refutation, citing heavily from the Bible and important theologians.
