Add multilingual support

[CarmelClark]

Is your feature request related to a problem? Please describe.
There is no support for the multilingual content provided by the Umami demo.

Describe the solution you'd like

• DruxtClient support for prefixes or langcodes
  • A node application should be able to request any resource by langcode with a fallback default langcode.
  • createResource (untested)
  • getCollection
  • getCollectionAll
  • getIndex
  • getRelated
  • getResource
  • updateResource (untested)
• Druxt modules support
  • DruxtBlock
    • DruxtBlockRegion isVisible method needs to support prefixes
  • DruxtBreadcrumb
  • DruxtEntity needs a langcode prop.
  • DruxtMenu
    • DruxtMenu needs a langcode prop.
    • DruxtMenu store needs support for prefix.
    • JSON:API Menu Items needs langcode support:
      • https://www.drupal.org/project/jsonapi_menu_items/issues/3192576
      • https://www.drupal.org/project/jsonapi_menu_items/issues/3260494
  • DruxtView
    • DruxtView needs a langcode prop.
    • JSON:API Views needs multilingual support in Decoupled Router integration: https://www.drupal.org/project/druxt/issues/3273228
• DruxtStore support for prefixes or langcodes
  • druxt/addResource; resource data is stored against prefix
  • druxt/getResource
  • addCollection
  • getCollection
• DruxtRouter support for prefixes or langcodes
  • Fetching the route shouldn't need to change, nor should the storage, as the langcode data is provided by the Decoupled Router with patch

    "drupal/decoupled_router": {
      "https://www.drupal.org/project/decoupled_router/issues/3111456#comment-14093342": "https://www.drupal.org/files/issues/2021-05-05/3111456-34.patch"
    }
    

  • Redirects need to work
    • Workaround: Disable router middleware
  • API proxy endpoint for langcode prefixes

Testing (in gitpod)

1. Open https://gitpod.io/#https://github.com/druxt/druxt.js/pull/422
2. Wait
3. cd examples/nuxt/druxt-site && yarn && yarn dev

Describe alternatives you've considered
No

Additional context

• Multilingual enabled backend: https://nginx.develop.demo-api-druxtjs-org.au2.amazee.io

• robedwards-cti@b89857e

• 

• https://demo-api.druxtjs.org/es

• https://demo.druxtjs.org/es (redirects to English).

• https://demo-api.druxtjs.org/en/jsonapi/configurable_language/configurable_language

[Decipher]

The JSON:API endpoints already support changing the langcode to get the multilingual resource.

[Decipher]

EN: https://demo-api.druxtjs.org/en/jsonapi/node/article

ES: https://demo-api.druxtjs.org/es/jsonapi/node/article

[Decipher]

Looks like you can get a translated version of the entire site (mostly) just by changing the endpoint in the nuxt.js.config:

export default {
  ...
  druxt: {
    baseUrl: 'https://demo-api.druxtjs.org',
    endpoint: '/es/jsonapi'
  }
}

[Decipher]

There's a patch for the Decoupled Router Drupal module related to multi-lingual support: https://www.drupal.org/project/decoupled_router/issues/3111456