In a new post to his blog, Vinu Thomas talks about a set of functions that can make your life easier when handling unicode strings - the mb_* methods of the mbstring extension.

When dealing with multiple languages and internalization in PHP, some of the default functions in PHP end up mangling up the unicode characters in PHP. This is evident when you have a lot of funny looking characters coming up on your web page instead of the actual characters. [...] There is an extensions called mbstring which you can install in PHP which gives you a set of functions which are unicode ( actually multibyte ) ready.

He mentions some of the replacements like mb_send_mail instead o fmail and mb_strlen instead of the usual strlen. Thankfully, there's a simple way to make use of these functions without having to replace a lot of code - a setting in your php.ini (mbstring.func_overload) that tells your application to seamlessly replace things behind the scenes.