Error · html-xml-lang-mismatch
Two different languages declared
Lighthouse / axe call it: HTML elements with lang and xml:lang must have the same base language · <html> element does not have an [xml:lang] attribute with the same base language as the [lang] attribute
The page declares one language in lang and another in xml:lang.
Who it leaves out: blind people (screen readers)
How to fix it
Make them match. Code included.
In the code
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Automated testing covers roughly half of WCAG criteria; a full conformance claim also requires manual review. Technical information, not legal advice.