Pedantic quibble (but why not be pedantic here?): "Mit Brennender Sorge" was not in Latin. Whether it was the first encyclical not to be in Latin, I can't say.

Also "Llewellyn is a professor at Wyoming Catholic College, and belongs to that select group of professors who consider themselves first and foremost teachers." It seems to me that such a field ought to make for that--there is always something to be gained by reexamining older texts, but it's not as if unknown books of Livy are flowing out of obscure libraries, as in Erasmus's day.