Populate lang attribute on root html element when translator is present.

[ktsimpso]

This issue is requesting an enhancement to Perseus. Details of the scope will be available in issue labels.
The user described the problem related to this request as follows:

Populate lang attribute on root html element when translator is present.

The user described the issue as follows:

Lighthouse Accessibility score recommends populating the lang attribute to help screen readers announce text correctly. See: https://dequeuniversity.com/rules/axe/4.4/html-has-lang?utm_source=lighthouse&utm_medium=devtools

Since Perseus should know the lang of the page when a translator is present, it should automatically populate this attribute.

• The author is willing to attempt an implementation: false

Tribble internal data

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[arctic-hen7]

This should be fairly trivial, since, according to MDN, the lang attribute accepts the same BCP-47 language tags, which means we can just use the locale strings Perseus already works with internally. Beta 20 is being released as I write this with a deployment fix, but this will go in beta 21, since there's no reason to delay this (the website will be used as a production validation that this appeases Lighthouse, since it uses i18n).

[ktsimpso]

Awesome, thanks! Will try this out when beta 21 releases.