🎙️ a11y: update html lang attribute

[jacobcolyvan]

Summary

Closes #3458

This implements approach discussed in #3458, which in sum is to:

• make sure the initial index html is returned by the server with the users preferred language.
• make sure we're updating the html lang attribute on change in the menu.

Client side, to do this I replaced managing lang choice in local storage with cookies. This meant I had to add the js-cookie package to the client. I looked at managing the cookies without the dependency, but I think this gives us a bit more reliability and sets us up to use cookies more in the future if we choose to do so.

This does however require users to re-choose their language as we're no longer using local storage to manage this data, so it introduces a minor breaking change. So once this update is installed users will need to re-choose their language (though it will fallback to the browser preferred language).

Server-side, this accesses the cookie in the request, opens the index.html file and replaces the lang attribute before returning it. This also add the cookie-parser package, but this is recommended by express.
This feels a little messy but I wasn't sure of another way to do it without adding a templating engine.

Change Type

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Testing

[Tested via serving the frontend via the api]:

• initial page load returns a html lang attribute w/ the browser language of the user .
• can choose a language in the settings, which will:
  • add a langcode cookie.
  • change the lang attribute in the markup.
  • no new local storage lang items are added.
• on page reload it will be return the langcode in the initial markup.

Test Configuration:

This does not work if you're running the frontend in dev.

Checklist

Please delete any irrelevant options.

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• My changes do not introduce new warnings
• Local unit tests pass with my changes
• I have written tests demonstrating that my changes are effective or that my feature works

[danny-avila]

Thank you for this and thanks for considering doing this without packages. Both are pretty lightweight so I'm okay with this approach

[jacobcolyvan]

Thanks @danny-avila, I've resolved those issues.
Let me know if you're after any other changes.