So much. It is surprising, I know. For instance, how about Descartes' very first book? Or Baumgarten's "Aesthetica", where he introduced the idea of "Aesthetics"? I talked to a scholar recently who said that it will probably never get translated, because there isn't the interest.
This. Even in Christian circles, many major works remain in Latin because publishers know they can't profitably commission the effort. This creates a situation in which for-profit publishers occasionally fund non-profit translation efforts to preserve the history.
For example, a shockingly small amount of John Calvin's works are translated into English. Regardless of what a person thinks of his theology, his influence on the rise of democracy in post-Reformation Europe and the Americas is staggering.
Most of his sermons and letters are still not in print in English, as well as a treatise on the Trinity, off the top of my head. Granted, as you point out, a large number of his works are in English but given his influence, it's surprising how many remain inaccessible.
There was a Latin collection that contained some of these works called the Corpus Reformatorum published in the 1800s.
