Why is having a lang attribute in a document significant for accessibility?

Having a lang attribute in a document is significant for accessibility primarily because it informs screen readers of the document's language. When a screen reader encounters the lang attribute, it can adjust its pronunciation and linguistic rules accordingly, ensuring that users who rely on these technologies receive the content in a way that is coherent and understandable. For instance, if a document is written in English, but includes a section in French, the screen reader can switch to the proper pronunciation and intonation for the French section only if the lang attribute is properly set. This tailoring greatly enhances the user experience for individuals with visual impairments or reading disabilities, ensuring that all users can access and comprehend the content effectively.