I'm using this dtd
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">
Error is for this attribute?
<html lang="en">
Should i remove this from DTD?
Just use
<doctype html>
. You're not using XML anyway, and the xml:lang attribute doesn't do anything in HTML.