> UK and Netherlands use an international keyboard with a tilda ~ key where the return key should be, and a backslash key where the left shift should be.

That is actually the original IBM PC XT layout from 1981: https://en.wikipedia.org/wiki/File:IBM_Model_F_XT.png

Then in 1984 USA moved to their own layout with the PC AT: https://en.wikipedia.org/wiki/File:IBM_Model_F_AT.png

But the rest of the world stayed with the original.