Martin Luther used several sources, he relied most on the Greek translation of the New Testament that Erasmus made based on Eastern editions, but his translation varied from the original.
What is more telling is that there were several approved Catholic editions in both High and Low German for more than 100 years prior to Luther’s translation. What helped Luther was living and writing at the time of the invention of movable type. Prior to this each page was engraved, or carved out of a plank of wood. The wood would have to be carved backward to produce an image that was printed correctly. With movable type pages could be rapidly set, cutting down the cost of printing a page, a short tract and a book, making them more easily availible.