Rocket Validator automatically scans your sites for accessibility issues using the W3C Validator,
hosted on our own servers and integrated into our web crawler.
HTML issues tagged as lang.
Instead of using the isolang attribute to define the language of the document, you can use lang with an ISO 639-1 two character code.
For example, for Portuguese:
Always use a language attribute on the <html> tag to declare the default language of the text in the page, using the lang property.
Based on the content of the document, the W3C validator thinks that it’s written in English. Consider explicitly specifying the language using the lang property.