Internationalization and Localization are concepts that all web sites and applications will have to deal with at some point. Why not design it form the start? Most people just don't think about it but in an increasingly global society, you need to. The earlier you design for it, the easier it is to do.
They continue on in this post on the Zend Developer Zone with a resource to get you thinking - an Internationalization Primer from Johnathan Snook (as printed in Digital Web Magazine). He looks at the basics you'll need to know when putting in multi-language support, including database designs and precompiling.