Thank you @Cantiger. So he will take Euro (and definitely anyway was going to take two more exams that can count for him) - the only outstanding question is if he needs to take Eng Lang. He put it on the list because it fills an esoteric requirement for a writing test at MIT, but is not taking a correlated course, or in any way committed to the exam via the school. It’s further complicated by the fact that Eng Lang is on a day when he would be working off-site, so he’d miss an entire day to take the exam. And it offers no credit at all to him at Princeton.
So, is the Common App list the be-all and end-all, or would these be enough reasons to take “all but Eng”? Would Princeton rescind or “be mad” if he takes all but one?