# The lang and xml:lang attributes on must match.
> Canonical HTML version: https://rocketvalidator.com/accessibility-validation/accesslint/0.16/readable/html-xml-lang-mismatch
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)
When an HTML document includes both `lang` and `xml:lang` attributes on the `` element, the two values must specify the same base language. If they differ, assistive technologies may not know which language declaration to trust. A screen reader could select the wrong speech synthesis voice, mispronouncing content throughout the entire page. This affects every screen reader user who visits the page.
The `lang` attribute is the standard way to declare a page's language in HTML5. The `xml:lang` attribute comes from XHTML and is only needed when serving documents as XML (with an `application/xhtml+xml` content type). In practice, most HTML5 pages do not need `xml:lang` at all. When both attributes are present, though, they must agree.
## Why this matters
WCAG success criterion 3.1.1 (Language of Page) at Level A requires that the default human language of a page can be programmatically determined. Screen readers rely on the language declaration to load the correct pronunciation rules. A mismatch between `lang` and `xml:lang` creates ambiguity: the screen reader may pick one value over the other depending on the browser or the assistive technology in use. The result is unpredictable behavior, and potentially an entire page read aloud in the wrong language.
## How to fix it
The simplest fix is to remove the `xml:lang` attribute entirely. HTML5 documents do not require it. If the document must be valid XHTML (served as `application/xhtml+xml`), keep both attributes but set them to the same language code.
Make sure the base language matches. For example, `lang="en-US"` and `xml:lang="en-GB"` are a mismatch even though both are English variants; the values must be identical.
## Examples
### Mismatched language attributes
The `lang` attribute says French, but `xml:lang` says English. A screen reader cannot reliably determine which is correct.
```html
Exemple
Bonjour le monde
```
### Fixed: remove xml:lang (preferred for HTML5)
Dropping `xml:lang` removes the ambiguity. The `lang` attribute alone is sufficient for HTML5.
```html
Exemple
Bonjour le monde
```
### Fixed: both attributes with matching values
If both attributes are needed (for example, in an XHTML document), they must have the same value.
```html
Exemple
Bonjour le monde
```