The page language must be a valid BCP-47 tag
Rule
html-lang-valid· Document, language & navigation · impact serious · Static + live
Why it matters
A malformed value (lang="english", lang="en_US") is not recognised, so AT cannot apply the right language profile.
How to fix
Use a well-formed BCP-47 tag: a 2–3 letter language subtag, hyphen-separated subtags (en, en-US, zh-Hant).
Example
<html lang="english">
<html lang="en">
WCAG success criteria
3.1.1 Language of Page — Level A
The default human language of the page must be set programmatically (<html lang>).
Standards
This rule contributes to the following standards:
WCAG A EN 301 549 Trusted Tester ACT
| Standard | Criteria |
|---|---|
| EN 301 549 | 9.3.1.1 |
| Trusted Tester v5 | 11.a |
| ACT (WCAG SC) | 3.1.1 |