The lang attribute on <html>

Set a valid BCP 47 language tag on the <html> element so screen readers, translators, search engines, and browsers know what language the page is in.

What it is

Every HTML document should declare its primary language on the root element using the lang attribute:

<html lang="en">

The value is a BCP 47 language tag — a short, standardised string that identifies a language and, optionally, a region or script. Examples: en, en-GB, nl, pt-BR, zh-Hant, de-AT.

Why it matters

The language of the page is metadata that many systems rely on:

Screen readers switch pronunciation engines based on lang. Without it, VoiceOver and NVDA read English text with a Dutch accent, or vice versa, making content unintelligible.
Browsers offer translation prompts ("Translate this page from French?") only when they know the source language.
Search engines use it as one signal for which audience to show the page to.
Spell checkers in <textarea> and contenteditable fields use the document language as their default.
CSS can match :lang(en-GB) to apply locale-specific typography (quotation marks, hyphenation).
WCAG 3.1.1 Level A requires the human language of every page to be programmatically determinable.

A missing lang is one of the most common accessibility failures, and one of the easiest to fix.

How to implement

Use a valid BCP 47 tag. The simplest form is just the two-letter ISO 639-1 language code:

<html lang="en">
<html lang="fr">
<html lang="ja">

Add a region only when it changes meaning — currency, spelling, or pronunciation:

<html lang="en-GB">   <!-- British English: "colour", "behaviour" -->
<html lang="en-US">   <!-- American English: "color", "behavior" -->
<html lang="pt-BR">   <!-- Brazilian Portuguese -->
<html lang="zh-Hant"> <!-- Traditional Chinese script -->

For sections of a page in a different language, use lang on a child element:

<p>The French call it <span lang="fr">pamplemousse</span>.</p>

For right-to-left scripts (Arabic, Hebrew), pair lang with dir:

<html lang="ar" dir="rtl">

Common mistakes

Omitting the attribute entirely. Many CMS templates ship without it.
Using made-up codes like lang="english" or lang="us". Only BCP 47 tags are valid.
Setting lang="en" on a Dutch site because the template was copied from an English boilerplate.
Over-specifying the region (lang="en-US" on a generic global English site is fine but rarely needed).
Forgetting to update lang on translated pages — every locale needs its own value.

Verification

View source: confirm <html lang="..."> is present and matches the actual content language.
Run document.documentElement.lang in DevTools.
Use an accessibility checker (axe, Lighthouse). Both flag missing or invalid lang.
Listen to the page with a screen reader and confirm pronunciation matches the language.