In the second trial before reaching the Grail, the clue is "The Word of God: Only in the footsteps of God will he proceed.". Indy says "The name of God........Jehovah". Being born and raised Catholic, I was confused the first time I saw this movie (which was when I was about 5 years old), because I had never heard the term "Jehovah" before. It wasn't until I took Theology II in my sophomore year of high school that I finally understood.
I'm not sure if it was in the Bible or just in ancient scripts, but God's name was written out as "YHWH", known as the tetragrammaton (there were no vowels in Ancient Hebrew). At that time, people refused to actually speak his name, which is where terms such as "Lord" came about, but that's beside the point. Now as far as I know, there are two translations of the tetragrammaton, depending on where the vowels are placed: "Yahweh", which was the one I was familiar with in the Catholic Church, and "Yehowah", which eventually became "Jehovah".
Now this is the part that might be considered a blooper. It was stated that the Grail was discovered by three knights of the First Crusade, which was launched by Pope Urban II in 1095. Since the Protestant Reformation did not occur until the 16th century, this means that there were no Protestants at the time of the First Crusade. Which means that "Yahweh" would have been the term in use, not "Jehovah"
Not trying to be really nitpicky about tiny errors in movies or anything, I was really more aiming to educate. Hope you found this interesting.