I have another "observation" to make.
During my time at university I had a very rare opportunity. A group of us went to the library (special appointment) to have a look at some really important works. I remember only two of them:
- "Philosophiæ Naturalis Principia Mathematica" by Sir Isaac Newton, published in 1687!
- some Introduction to Geometry.
The second one was a smallish piece, and I could read the first few paragraphs: "A point is a nothing (has no extent in dimension). A (straight) line consists of points ..." I could read the text and understand it to some extent. It was written in Latin.
So my point is this: at other times, other languages were the "lingua franca" of some large region. It does change over time, provided you are tuning your time scale and patience.
Cheers,
~ew