[vurpo]

It would need a more complex solution than that. For example, this is the website of a local bus company where I live:

http://åbus.fi

The characters are from the Latin character set, but non-ASCII. Highlighting the Å in red would look pretty confusing. And in many countries you want the entire domain name written in non-ASCII characters, depending on the language. E.g. websites in Russia, China, India, etc...