Access: [4.3.1.1]: language not identified (Priority 3)

Cause:

Identify the primary language of each document to ensure that clients automatically retrieve web pages in their preferred language. Language can be specified either through meta tag.

Example:

Good
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head>
	<title>aert1.0/4.3.1 - The HTML element does not contain a lang attribute</title>
</head>
<body>
</body>
</html>
Good
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
	<title>Language identified.</title>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<meta http-equiv="Content-Language" content="EN" />
</head>
<body>
</body>
</html>

Solution:

Specify the language of your document using at least one of the following:

References: