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.
I've recently been ranting a lot about primary buttons. But people often don't understand what they are.
In my early days as a designer, I thought it just meant adding class="btn-primary" to my markup to make it pretty and blue, and this is a common mistake.
A lot of people make this mistake and litter the Internet with bad design which is confusing for the people that have to use it. Some of my early contributions are still out there causing a nuisance. Sorry.