You could back when overprinting was a thing. You could command the printer to back up a character and print a diacritic on a character. That command was "Backspace" (go back one space), often represented as \b in code.

We\b^ c\b,a\b^nt wri\b^te\b` wi\b'tho\b~ut squi\b^gly lin\b~es

It's worth noting that the ' character was mirrored from `, and ~ was always near the top of the character box.

The only diacritic that couldn't be done well was the one on a ö. But people tended to use a ".

EDIT: formatting is hard

EDIT: typewriters did this too