3.1.1 Language of Page
Official description of the success criterion
The default human language of each Web page can be programmatically determined.
What to do?
Specify the default language of the web page.
Why is it important?
Assists screen readers and other assistive technologies in reading the content correctly.
Common pitfalls
Often content management systems provide this functionality by default. If the user inputs content in the wrong language, for example, if they select the wrong page language, then this might be a problem.
Sometimes this type of implementation is done on purpose if a full language version is not deemed necessary and they "just add one page in another language". This is not ok. If this type of approach is desired, then the content in a different language must be marked with the lang attribute as required by criterion 3.1.2.
How to test for it?
Check if the page has a lang attribute in the <html> element. Automated tools can catch issues with this.