Using the language attribute to make your website accessible
Excerpt:
There's a couple of criteria in the Web Content Accessibility Guidelines that I see catching people out time and time again. 3.1.1 Language of page and 3.1.2 Language of parts.
These two criteria are important, because they help screen readers to read out the language correctly. If your page is set to English, but some of your content is not English, then the screen reader is just going to attempt to pronounce it in English anyway, which can lead to some pretty weird results.
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