The use of a meta element in the document head with the http-equiv attribute set to Content-Language is not mentioned in the HTML specification at all, and yet much of the informal guidance out on the Web about how to declare language for your HTML suggests its use, and some well-known HTML authoring tools create such elements when you specify language information using dialog boxes.

Unfortunately, there is little if any evidence that any mainstream browsers recognise such declarations for implementation of text-processing features. Nor is there much evidence of search engines using this information as meta-data about the document.

For this reason, it seems wise to avoid the use of this approach for now.

Since the arguments of the content attribute on the meta element allow for multiple languages to be expressed, this approach would seem to lend itself to declaration of primary language metadata rather than text-processing language. As such, it is the only currently available mechanism for authors to declare such metadata inside the document, and therefore potentially useful. To what extent metadata users use the information is still not clear, however. It is also possible to argue whether it makes sense to have metadata inside the document.