When I saw the recent kits of various 1/35 rail vehicles from Trumpeter, I started wondering about how similar civilian railroad vehicles of different nations seemed to look. For instance, would the German freight cars (barring markings) have been the same as in prewar Poland or the Soviet Union? Russia did build a railroad in northern China which they later sold to that nation.

See my comment.
https://armorama.kitmaker.net/forums/147698#1235591

Thanks, but I was thinking not only of rail gauges. I was thinking of overall car design, such as width, length, bogie design, brake systems, etc. Barring gauge width, how similar were the railroad cars?

I used to buy a lot of Piko Ho railroad cars in the former East Germany. There was not much difference in the older era German, East German, and French railroad cars they offered. Of course, living there in the 80's, there were still a lot of these old wagons still in use, but I didn't have much to compare them to. I will say that the cars in Iraq appear to have been very similar, pulled by Chinse locomotives bearing a ver strong resemblance to Russian ones. British cars (probably not what you're trying to model) looked decidedly different.