Well, there's almost no string handling built-in to PHP as a language at all, it's just provided as part of the standard library. So instead of using one part of the library (the standard string functions), you use another (the mb_* string functions.) I don't really see how that's a hack. The one thing that could go wrong is if you don't have the mb_* extension, but that's easily rectified, and hasn't been something I've seen in the wild in the past few years.

I'm not saying PHP's UTF-8 handling is great by any means, but the claim was that it's "nearly impossible." I'm suggesting that one should instead say "Building a UTF-8 compliant site in PHP is annoying, and requires more work than one would prefer, but if you do a bit of research, it's not that hard."