Translate Entity field labels

CategoryType.php

<?php
namespace Bkv\Bundle\LbwBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Translation\Translator;
use Symfony\Component\Validator\Constraints\NotBlank;

class CategoryType extends AbstractType
{
    /**
     * @var Translator
     */
    private $translator;

    public function __construct(Translator $translator)
    {
        $this->translator = $translator;
    }

    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $translator = $this->translator;
        $builder
            ->add('category', 'entity', [
                'label'         => 'Choose a category',
                'class'         => 'Model:Category',
                'expanded'      => true,
                // The solution
                'choice_translation_domain' => true,
            ])
    }

    /**
     * Returns the name of this type.
     *
     * @return string The name of this type
     */
    public function getName()
    {
        return 'bkv_lbw_category';
    }
}