From Dynamically Typed:

i18n in PHP is largely a mess today, to the point where Joel Spolsky singled it out last year with: "When I discovered that the popular web development tool PHP has almost complete ignorance of character encoding issues, blithely using 8 bits for characters, making it darn near impossible to develop good international web applications, I thought, enough is enough."

Note this response from Scott Reynen, looking at solutions implemented in PHP. Anyway, looks like there's a chance things may be about to get better. Check out this interesting message on Zend...

With several comments already posted, this seems to be an interesting little topic. PHP really could benefit from more i18n support (internationalization) built-in...