TYPO3 Core

Please add proper reproduction instructions. How to define the translation file, etc. thanks (eg. links to docs or so)

Here's our usecase: we wanted to re-use the label and option labels of a select field, so we added a custom prototype which extends SingleSelect:

TYPO3:
  CMS:
    Form:
      prototypes:
        standard:
          formEngine:
            translationFile:
              - EXT:form/Resources/Private/Language/Database.xlf
              - EXT:foo/Resources/Private/Language/Extensions/Form/locallang_db.xlf

          formElementsDefinition:
            CustomSelect:
              __inheritances:
                10: 'TYPO3.CMS.Form.prototypes.standard.formElementsDefinition.SingleSelect'
              renderingOptions:
                templateName: SingleSelect

Now we use this prototype multiple times in our form definition:

# ...
renderables:
  page:
    identifier: default
    type: Page
    renderables:
      - &custom
        identifier: custom1
        type: CustomSelect
        label: Custom select label
        properties:
          options:
            1: First
            2: Second
      - <<: *custom
        identifier: custom2

Now we use the following e.g. in the EXT:foo/Resources/Private/Language/Extensions/Form/de.locallang_db.xlf file:

<!-- ... -->
<trans-unit id="element.CustomSelect.properties.label">
  <source>Custom select label</source>
  <target>Eigenes Auswahl-Label</target>
</trans-unit>

<trans-unit id="element.CustomSelect.properties.options.1">
  <source>First</source>
  <target>Erstes</target>
</trans-unit>

<trans-unit id="element.CustomSelect.properties.options.2">
  <source>Second</source>
  <target>Zweites</target>
</trans-unit>
<!-- ... -->

Without this change, we'd need to provide translation for every single field identifier.

Patch set 1 for branch TYPO3_8-7 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/54950