Config parsing fails when i18n is set to duplicate

[privatemaker]

Describe the bug

As per #7291 upon recently trying to configure a i18n site with the new i18n: duplicate value on a per-field basis as per the i18n Documentation, I discovered it causes my config to fail to parse.

Expected behavior

Setting i18n: duplicate should not cause config to fail to parse and should duplicate fields in a read-only fashion in the cloned page.

Screenshots

Applicable Versions:

• Decap CMS version: decap-cms 3.4.0
• Git provider: GitLab
• OS: Linux
• Browser version Firefox 115.14
• Site generator: Hugo
• Decap Setup: Hugo Module headless-cms

CMS configuration

  locale: "en"
  i18n:
    structure: multiple_files
    locales: [en, de]
    default_locale: en
  slug:
    encoding: "ascii"
    clean_accents: true
    sanitize_replacement: "-"
  collections:
    - name: "blog"
      label: "Blog"
      label_singular: "Blog"
      folder: "content/blog"
      path: "{{slug}}"
      widget: "list"
      create: true
      i18n: true
      editor:
        preview: true
      preview_path: "blog/{{slug}}"
      media_folder: '/static/uploads'
      public_folder: '/uploads'
      fields:
        - label: "Title"
          name: "title"
          widget: "string"
          i18n: true
        - label: "Draft"
          name: "draft"
          widget: "boolean"
          default: true
          i18n: true
        - label: "Image"
          name: "banner"
          widget: "image"
          required: false
          default: "/uploads/placeholder.jpg"
          choose_url: true
          media_folder: '/static/uploads'
          public_folder: '/uploads'
          i18n: true

If I change any of the i18n: true values in the fields to i18n: duplicate I get the broken config parsing error shown above.

[martinjagodic]

@privatemaker it seems that the problem is with the widget list. This one does not support i18n: duplicate. Itself and all its children should thus have i18n: true.

This is mentioned in docs like this:

List widgets only support i18n: true. i18n configuration on sub fields is ignored.

I would say that the docs are ok, but we could improve the error message.

[privatemaker]

Thanks for investigating. I did get it working by trial and error of eliminating all instances of it and slow re-adding on different fields. But this is a bit random and wacky.

So, I think the docs could be improved a bit and will send a pull-request 😄