<html> element does not have a [lang] attribute
Understanding the language of the website
79% of my survey of 100 Webflow Websites had this error.
If you are a Canadian screen reader user, this issue might cause you problems. If you have the screen reader set to French, and you visit a site written in English, you will hear the text read in a French accent. It’s important to set the two-letter code for the main language of the website. Obviously it's not just Canadians who have this problem. Many Americans will access the web in English or Spanish. There are many countries which have more than one official language.
How to fix it
In Webflow you simply go to Project Settings, Custom Code > Advanced Settings > Language Code.
You need to add a standard 2-letter code.
It would be great if Webflow set this up as part of the workflow, rather than hiding it away in Custom Code.
Google Lighthouse says
To ensure correct pronunciation, screen readers use a different sound library for each language they support. Screen readers can switch between these language libraries easily, but only if a web page specifies which language to read for a given piece of content. If a page doesn't specify a language for the <html> element, a screen reader assumes the page is in the default language that the user chose when setting up the screen reader, often making it impossible to understand the content.