The HTML lang attribute specifies the language of your website. This attribute is important SEO-wise as it makes a website more accessible:
Search engines use the language attribute to return language-specific search results
Screen reading tools use this attribute to recognize the language and provide the correct accent and pronunciation while reading website texts
You can add a language attribute by selecting the preferred language in the general SEO settings. You'll be prompted with the pop-up asking you to specify the following:
Business or brand name – it will be used for the general meta title of your website; you can edit it later
Website's default language; you can edit it later:
You can also dismiss the pop-up (click X in the top-right corner), click the ← arrow in the top-left to get back to the general SEO settings window, and specify your website's default language here:
Finally, update your website.