See, it just broke when UTF-8 was interpreted as ASCII. It's entirely possible to treat bytes as bytes and leave encoding out of it for the vast majority of programs. If you're dealing with text editing and so on,
then you
know you need to be UTF-8 aware, and the broken programs would still be broken in either language.
The visibility of the errors is a minor point, but I think it more appropriate that it be solved by e.g. the windowing toolkit API.