What it is
Inconsistent or invalid language codes across the html lang attribute, hreflang and content confuse language handling. Codes should be valid and consistent everywhere. Wrong language codes. Confuses language handling/a11y. Use valid codes consistently. Low-medium. Inferred.
Why does mixed/invalid lang codes matter for AI search?
Confuses language handling/a11y.
How do you fix it?
Use valid codes consistently.
How do you find it on your site?
- Review the lang attribute, hreflang and any locale codes.
- Validate them against ISO standards.
- Make them consistent and correct across the page and site.
- Re-validate.
Which ranking and citation factors does it touch?
Invalid or mismatched lang codes undermine language targeting and accessibility. Consistent, valid codes keep it reliable.
What is the impact?
Low-medium. Inferred.
What is the evidence?
Valid language declaration. Google Search Central, Tell Google about localized versions (hreflang); W3C, Web Content Accessibility Guidelines (WCAG) 2.2
Sources
Frequently asked questions about mixed/invalid lang codes
What does "Mixed/invalid lang codes" mean?
Wrong language codes.
How do you fix mixed/invalid lang codes?
Use valid codes consistently.