Add embed to changeset manually

I’m trying to implement create/update actions where I manually create the changeset for the embed. This is what I currently tried, but the creation fails with an error, because the translations are missing (Ash.Error.Changes.Required)

attributes do
  attribute :translations, __MODULE__.Translations, private?: true, allow_nil?: false
end

create :create do
  primary? true

  change &cast_translations/2 
end

defp cast_translations(changeset, context) do
  translations_changeset =
    Ash.Changeset.new(
      changeset.data.translations || __MODULE__.Translations,
      changeset.params
    )

  Ash.Changeset.set_argument(changeset, :translations, translations_changeset)
end