How many professors in EU can still read Latin in 1950? And how about 2000? I know many scientific literature were written in Latin in the past.
First of all "can read" must be defined more precisely. Many math professors in Europe whom I know had some Latin in school and can read a page from Euler, when necessary. But they certainly cannot read and enjoy Latin poetry.
I never had any formal course of Latin, but I studied French, and also can understand 18 century mathematical texts in Latin with some efforts and perhaps with the help of a dictionary.
It is true that much scientific literature, especially in mathematics was written in Latin until 19th century. But this does not mean that an average modern mathematician reads it. Those who need to read much of it just learn Latin. I knew one mathematician who learned Latin with the special purpose to read Jacobi's works. But this is a rare exception. Most modern mathematicians read only modern literature. Or translations to modern languages.
I agree with Alexandre: professors of science and mathematics read mostly the current literature, the vast majority of which is in English.
However, in this forum, when the OP says "professors", he may mean professors of History of Science or History of Mathematics. In that case, depending on what era and what region of the world they study, other languages may be needed.
I heard a talk a few years ago by someone studying some topic in the history of geometry. But he had come to an impasse because he did not read Arabic.