On the ThinkPHP blog, Florian Eibeck has posted an overview of some key things to consider when internationalizing your application/website.

The biggest problem is that most developers lack knowledge about Internationalisation, Localisation, Character encodings, Unicode and all those terms connected with multilingualism. The following article should give you a basic understanding and show you how to avoid those funny characters.

He defines a few terms - internationalization, ASCII, unicode and the UTF-8/ISO-8859 character sets. He mentions how to accept the utf-8 string into your application and how to use it in both PHP and store it in a MySQL database.