Page does not declare a language
What it means
These pages have no lang attribute on <html>. A screen reader then guesses, and reads English in a French accent or the reverse, which ranges from irritating to incomprehensible.
How to fix it
Add lang to the <html> element: <html lang="en-GB">. Mark any passage in another language with its own lang too. This is one attribute, it takes a minute, and it is WCAG 3.1.1 at level A.
Finding it in CrawlStat
After a crawl, open Issues and pick Page does not declare a language. Click Show all in Pages to filter the Pages table to the affected pages, or Export affected to hand the list to whoever owns the fix. Audit ID: a11y_page_without_lang.