ot_typo3/ot_templating/Configuration/Form/CustomFormSetup.yaml

# Configures the path of the directory containing the extension's forms
TYPO3:
  CMS:
    Form:
      persistenceManager:
        allowSaveToExtensionPaths: false
        allowDeleteFromExtensionPaths: false
        allowedExtensionPaths:
          20: EXT:ot_templating/Resources/Private/Forms/
      prototypes:
        standard:
          formElementsDefinition:
            Form:
              renderingOptions:
                translation:
                  # <!!!> 'translationFile' becomes 'translationFiles' in typo10+
                  translationFile:
                    # Default translation file of EXT:form (always needed, but can be remove in typo10+)
                    10: 'EXT:form/Resources/Private/Language/locallang.xlf'
                    # Load custom translation file(s)
                    20: 'EXT:ot_templating/Resources/Private/Language/Form/locallang.xlf'