[sebastian]

A good way to fix this would be coloring all Unicode characters in the URL bar.

[deckiedan]

That doesn't work for colour blindness, or languages that use extended Latin alphabet. Some letters of a word would be one colour and others another.

[Zuider]

The Unicode letters could be darker, which would still be visible if you are color blind. If the highlighted characters were not ones that would be expected to be represented by Unicode, i.e. if they were not special characters or diacritics, than that should raise an alarm, especially if the user was familiar with how the genuine URL looked.

[sebastian]

Different colour + underlined.

[krallja]

All letters are Unicode.