3.1. Provide the primary language of the page with the lang attribute on the <html> tag
In order to ensure good rendering of text content, the primary language must be declared on each page.
Use the lang attribute on the <html> tag.
For example, for an English page use:
<html lang="en">
Tip
To populate the lang attribute, a two-letter language code (or, if it is not available, three-letter code) must be used.
Some common codes are:
enfor English.frfor French.esfor Spanish.defor German.itfor Italian.
The others are available here: exhaustive list of authorized language codes.