Primary language of the page is not defined
The primary language of the page MUST be identified accurately on the <html> element.
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.
Fix this issue by identifying the primary language of the document in the opening <html> element using the lang attribute.
In the following example, the two-letter code "en" specifies English as the primary language of the document. <html lang="en">