In plain English
Your page is written in a language, and the browser needs to be told which one.
That is done with a tiny attribute on the very first tag: <html lang="en">.
Screen readers use it to pick the correct pronunciation. Leave it off, and an English store might be read aloud with French or German pronunciation rules, turning your product descriptions into gibberish. It is a one-line fix with an outsized impact.
Who this is for
- Screen-reader users, who get correct pronunciation only when the language is declared.
- Translation tools and search engines, which use it to understand and process your content.
What “good” looks like
One attribute, on the root element.
<!-- Good -->
<html lang="en">
<!-- Bad: no language declared -->
<html>If part of the page is in another language (say a French product name), mark
just that part with its own lang (that is the related criterion 3.1.2).
Where stores get it wrong
Custom themes or landing pages that ship the <html> tag with no lang, and
pages built by tools that forget it. It takes seconds to check: view source and
look at the first line. Missing lang shows up on the
common failures list.