No language declaration
What this means
The response carries no Content-Language header and the page declares no hreflang tags, so nothing states the page's language to crawlers or assistive technology.
How to fix it
Set a lang attribute on the html element (for example <html lang="en">), and send a Content-Language header where your stack makes it easy.
Fix effort
This check is auto-fixable: the change can be written and validated automatically, so CrawlX can open it as a pull request for review.
Authoritative source
https://www.w3.org/International/questions/qa-html-language-declarations
Related checks
More in Accessibility
Find every page this affects
CrawlX runs this check — and 161 others — across your whole site, ranks the findings by estimated impact, and opens the fixable ones as pull requests. Free for 500 URLs.