3.1.1 Language of Page

In Plain Language

Every web page must declare its primary language using the lang attribute on the <html> element. This tells screen readers which language engine and pronunciation rules to use when reading the page aloud.

Without it, a screen reader may try to read French text with English pronunciation rules, making it incomprehensible.

Why It Matters

Screen readers use the lang attribute to switch between language-specific pronunciation engines -- without it, every word is mangled through the wrong rules.
Browsers use the language declaration for proper text rendering, including hyphenation, quotation marks, and font selection.
Translation tools rely on the lang attribute to detect the source language before offering translations.
This is a foundational requirement -- simple to implement but still missing on 13.5% of home pages surveyed.

Examples

Do: Declare the page language

<!DOCTYPE html>
<html lang="en">
  <head>...</head>
  <body>...</body>
</html>

Don't: Missing lang attribute

How to Fix It

Add lang to the <html> element. Use a valid BCP 47 language subtag: en for English, es for Spanish, fr for French, zh for Chinese, etc.
Be specific when needed. Use regional subtags like en-US vs en-GB when pronunciation differences matter for your content.
Mark language changes inline. When a passage is in a different language than the page, use the lang attribute on the containing element: <span lang="fr">bonjour</span>.
Avoid common mistakes. Do not use lang="javascript", lang="utf-8", or other invalid values. The attribute requires a valid language code, not a programming language or encoding.