I was reading this answer which referenced a number of 18th century publications which capitalised their non-proper nouns:
In 1769, in "The Microscope made easy":
"Mention having been often made of a Screen to throw the Images of Objects on, it is proper to inform the Reader, that such a Screen is usually composed of a Sheet of the largest Elephant Paper, strained on a frame, which slides up or down, or turns about at Pleasure on a round wooden Pillar, in the Manner of some Fire-screens. Larger Screens are likewise made sometimes with several Sheets of the same Paper pasted together on Cloth, and let down from the Ceiling with a Roller, like a large Map"
1742, in Micrographia Nova: Or, a New Treatise on the Microscope
Thus if a lens of about 6, 8, or 10 Feet focal Distance, be fix'd in the Scioptric Ball, then if the Sun shine strongly on the Objects without, opposite to the Window, the Images of all will be distinctly form'd on a Wall or large Sheet or Screen of white Paper placed in the Focus of the Glass; the result of which will be a beautiful and most perfect Piece of Perspective, if the Objects are Buildings, &c. but Gardens, Fields, Meadows, Hills, Groves &c. present you with a most exquisite and inimitable Landscape
This is still the case for the German language, but English lost this property somewhere between that time and now.
When did English stop requiring capitalisation of non-proper nouns?
