If you want to declare primary language metadata for the pages you serve, do so by getting the server to send the information in the HTTP header.

Using the HTTP Content-Language header entails potential issues related to the maintenance and use of server-side information. Many authors may find it difficult to access server settings, particularly when dealing with an ISP. Also, pages may not always be located on servers. So this approach is not a solution that is always available.

In theory, it might be good to declare primary language information in a meta element. This is easy for authors to add, and would remain with the document if not viewed from the server. In practise, however, it seems that this is little used at the moment.

If your document has multiple primary languages, both of these methods allow you to supply a comma-separated list of languages as the value.