public function buildForm(FormBuilderInterface $builder, array $options): void
{
    // disable non-default locales which have empty translation objects (user did not fill anything in)
    $builder->addEventListener(FormEvents::SUBMIT, function (FormEvent $event): void {
        $collection = $event->getData();
        assert($collection instanceof Collection);
    
        foreach ($event->getForm() as $child) {
            $translation = $child->getData();
            assert($translation instanceof TranslationInterface);
    
            $required = $translation->getLocale() === $this->defaultLocale || !$this->isTranslationEmpty($translation);
            if($required) {
                $config = $child->getConfig();
                $ref = new ReflectionClass(FormConfigBuilder::class);
    
                $reqProp = $ref->getProperty('required');
                $reqProp->setValue($config, true);
    
                $optionsProp = $ref->getProperty('options');
                $childOptions = $optionsProp->getValue($config);
                $childOptions['required'] = true;
                $optionsProp->setValue($config, $childOptions);
            } else {
                $ref = new ReflectionClass($child::class);
                $submittedProp = $ref->getProperty('submitted');
                $submittedProp->setValue($child, false);
            }
        }
    });
}

public function getParent(): string
{
    return CollectionType::class;
}