Unable to translate paragraphs – non-translatable fields are visible and cause errors

Problem/Motivation

When creating translations of paragraphs, non-translatable fields are still visible on the translation form, even when they are configured to be hidden. Editing them results in an error.

Steps to reproduce

Preparation

1. Set up a multilingual Drupal 10/11 site with at least 2 languages.
2. Enable Layout Paragraphs (v2 or v3) for the Page content type.
3. Allow the Page content type to be translatable.
4. Create a paragraph type with:
   - a translatable text field
   - a non-translatable boolean field
5. In translation settings:
   - Show language selector on create and edit pages → FALSE
   - Hide non-translatable fields on translation forms → TRUE

Workflow

1. Create a node of type Page and add the paragraph.
2. Click Add translation of the Page node.

Issue 1:

The non-translatable field is visible, but it should be hidden (since “Hide non-translatable fields on translation forms = TRUE”).

3. Change the paragraph’s text field (translatable) and boolean field (non-translatable). Save.

Issue 2:

Error message appears:

Non-translatable fields can only be changed when updating the original language.

Notes

This happens only when creating a new translation of a paragraph.
Once the paragraph has been translated at least once, you can update non-translatable fields from a node translation, and the changes are reflected across all translations (as expected).