All WCAG criteria
WCAG 2.1·Understandable·3.1 Readable
3.1.1 Language of Page
Level AThe default human language of the page must be programmatically determined.
Why it matters
Screen readers use lang to choose the right pronunciation engine — wrong lang sounds like gibberish.
Common failure
<html>
Accessible version
<html lang="en">
How OnlyEnable handles this
Automatically remediated. OnlyEnable sets document.documentElement.lang on load if missing.