Value of the lang attribute is not valid
lang-invalid
Rule
The primary language of the page MUST be identified with a valid value on the <html> element.
Background
Most screen readers can read several different languages. Screen reader users select a default language when installing and configuring their screen reader. If no language is specified in the HTML document, the screen reader will read the document in the user's default language with a pronunciation that often makes it impossible to understand the content, if default language doesn't match the document language. Screen reader users who speak only one language will probably access websites only in their native language, so they won't experience any language issues. People that speak more than one language though will likely access websites in more than one language. They will want to hear each language read correctly, with the proper accent and pronunciation. When the language of the page is correctly identified, screen readers will know which language library to use.
How to Fix
Fix this issue by providing a correct and valid lang attribute value.
In the following example, the two-letter code "en" specifies English as the primary language of the document. <html lang="en">