An an aspect of internaltionalization (i18n) I often skip over is localization (l10n) or customizing text (e.g. spelling, transliteration conventions, prices in the correct currency, date stamping in the correct format etc). If localization is something you need to have on a Web site, you may want to start at the Unicode CLDR page (http://cldr.unicode.org/) which compiles a variety of charts and some guides.
There are other resources available including several from IBM listed below:
These resources are generally aimed for the programmer audience, but there are interesting nuggets for the non-programmer as well.