A Symfony form extension to generate label (see http://www.elao.com/blog/non-classe/a-nice-way-of-handing-form-label-translation.html for another solution)

FormatLabelTypeExtension.php

<?php

namespace Your\Namespace\Forms\Extension;

use Symfony\Component\Form\AbstractTypeExtension;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Form\FormView;
use Symfony\Component\Form\FormInterface;

/**
 * Class FormatLabelTypeExtension is used to format all Form label by default.
 *
 * It uses <form1>.<field name>.label
 * Or If there are child :
 *
 *
 */
class FormatLabelTypeExtension extends AbstractTypeExtension
{
    /**
     *
     * @param FormView      $view
     * @param FormInterface $form
     * @param array         $options
     */
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        // Generate a label only for field which do not have a label already set
        if (is_null($view->vars['label']) === true) {
            // Not very nice code
            // Get all parents form name to generate the prefix
            $parent = $form->getParent();
            $formNames = array();
            while ($parent !== null) {
                $name = $parent->getName();
                $formNames[] = $name;
                $parent = $parent->getParent();
            }

            // Need to reverse order
            $prefix = implode(array_reverse($formNames), '.');

            $formName = $form->getName();

            if ($form->getParent() instanceof FormInterface) {
                // If parent form is a CollectionType, replace integer value by entry
                $formType = $form->getParent()->getConfig()->getType()->getInnerType();
                if ($formType instanceof CollectionType) {
                    $formName = 'entry';
                }
            }

            $view->vars['label'] = sprintf('%s.%s.label', $prefix, $formName);
        }
    }

    public function getExtendedType()
    {
        return 'form';
    }
}

FormatLabelTypeExtensionTest.php

<?php

namespace Your\Namespace\Tests\Forms\Extension;

use Symfony\Component\Form\Forms;
use Symfony\Component\Form\FormFactoryInterface;

use Your\Namespace\Forms\Extension\FormatLabelTypeExtension;

class FormatLabelTypeExtensionTest extends \PHPUnit_Framework_TestCase
{
    private $factory;

    protected function setUp()
    {
        /** @var FormFactoryInterface factory */
        $this->factory = Forms::createFormFactoryBuilder()
            ->addTypeExtension(new FormatLabelTypeExtension())
            ->getFormFactory();
    }

    public function testLabelIsPrefixedByRootFormNameSuffixedByLabel()
    {
        $parent = $this->factory->createNamed('my_name_form', 'form');
        $parent->add($this->factory->createNamed('field1', 'text', null, array(
            'auto_initialize' => false
        )));
        $field = $parent->get('field1');
        $this->assertEquals(
            'my_name_form.field1.label',
            $field->createView()->vars['label']
        );
    }

    public function testFormWithChild()
    {
        $parent = $this->factory->createNamed('my_name_form', 'form');
        $parent->add($this->factory->createNamed('child1', 'form', null, array(
            'auto_initialize' => false
        )));
        $child1 = $parent->get('child1');
        $child1->add($this->factory->createNamed('field1', 'text', null, array(
            'auto_initialize' => false
        )));
        $field = $child1->get('field1');
        $this->assertEquals(
            'my_name_form.child1.field1.label',
            $field->createView()->vars['label']
        );
    }

    /**
     * Label for collection type replace integer value by entry
     * Instead of my_name_form.fieldList.0.label or my_name_form.fieldList.1.label
     * get my_name_form.fieldList.entry.label
     */
    public function testFormWithCollection()
    {
        $parent = $this->factory->createNamed('my_name_form', 'form');
        $parent->add(
            $this->factory->createNamed(
                'fieldList',
                'collection',
                array('a', 'b'),
                array(
                    'type' => 'text',
                    'auto_initialize' => false
                )
            )
        );

        $field = $parent->get('fieldList');
        $this->assertEquals(
            'my_name_form.fieldList.entry.label',
            $field->createView()->children[0]->vars['label']
        );
        $this->assertEquals(
            'my_name_form.fieldList.entry.label',
            $field->createView()->children[1]->vars['label']
        );
    }

}