lang attribute must have a valid value
The interface language statement (lang attribute) allows user agents, in general, and assistive technologies, in particular, to parse and read the content more accurately. Internet technologies use the "ISO 639-1 language codes". Any value of the lang attribute that is not part of this list is not valid and should be replaced with a valid one.
12 <!DOCTYPE html>34✓ <html lang="en">5 <!-- html content -->6 </html>78✗ <html lang="english">9 <!-- html content -->10 </html>11
How Users Are Affected
Assistive technologies may misread or mispronounce the content, and therefore be misleading the user or even prevent him from understanding and using the interface properly.
WCAG Success criteria
This issue might cause elements to fail one or more of the following Success criteria:
3.1.2 Language of Parts (AA)