How to change the HTML Language Code Reference
With uSkinned Site Builder for Umbraco, this couldn't simpler. There is no need to update any code, we've included this setting within the CMS itself.
You should always include the lang attribute inside the <html> tag, to declare the language of the Web page. This is meant to assist search engines and browsers. You can see a full list of the references here: https://www.w3schools.com/tags/ref_language_codes.asp
Login to the CMS.
In the left-hand tree menu, go to Global.
On the right-hand side, select Settings.
On the "General" tab, scroll to "Override language code reference".
Enter the correct code here e.g. en
At the bottom right-hand side, Save and publish.