Marking Up Language
The World Wide Web Consortium has updated their document called Authoring Techniques for XHTML & HTML Internationalization: Specifying the language of content 1.0. This document provides advice on how to provide access to the language(s) you are using within a web document. From the Introduction:
This document provides guidance for developers of HTML that enables support for international deployment. Enabling international deployment is the responsibility of all content authors, not just localization groups or vendors, and is relevant from the very start of development. Ignoring the advice in this document, or relegating it to a later phase in the development process, will only add unnecessary costs and resource issues at a later date.