Set fallback locale symfony translation

Question

I have to translate an email in many languages. But for some version of this project, some locale do not exists.

Requirements is: if locale does not exist on the project, then use English.

Issue is that by default, translator use FR as fallback:

framework:
   translator:      { fallbacks: ["%locale%"] }

So when I try to translate to a locale that does not exist, it fallback to French instead of English.

Is there a way to check if locale is available before translation?

EDIT : Fallback to English is used only for one specific case

EDIT 2:

{{ 'contact.prefix' | trans }}

Answer 1

The Twig trans extension have some parameters

{{ message|trans(arguments = [], domain = null, locale = null) }}

https://symfony.com/doc/current/reference/twig_reference.html#trans

So I would check the local in twig at the start of my email template and if it's not a 'valide' one I would force english using the local parameter of the trans extension

Answer 2

May be someone will need my solution because I think it is boring to write

{{ message|trans(arguments = [], domain = null, locale = null) }}

For every translation.

First, I have created a service to check if the translation for a given locale is available :

use Symfony\Component\HttpKernel\KernelInterface;

class LocaleChecker
{
    const TRANSLATE_FILE_PATTERN = 'mail.%s.yml';

    /**
     * @var KernelInterface
    */
    private $storage;

    public function __construct(KernelInterface $kernel)
    {
        $this->storage = $kernel;
    }

    /**
     * @param string $locale
     *
     * @return bool
     */
    public function isLocaleExist(string $locale)
    {
        $filename = sprintf(self::TRANSLATE_FILE_PATTERN, $locale);
        $path = sprintf('%s%s', $this->storage->getTranslationsDir(), $filename);

        return file_exists($path);
    }
}

Then I have created a twig extension to do the job for me :

<?
use FrontBundle\Service\Translate\LocaleChecker;
use Symfony\Component\Translation\TranslatorInterface;

class FallbackEnglishExtension extends \Twig_Extension
{
    /**
     * @var LocaleChecker
     */
    private $localeChecker;

    /**
     * @var TranslatorInterface
     */
    private $translator;

    public function __construct(LocaleChecker $localeChecker, TranslatorInterface $translator)
    {
        $this->localeChecker = $localeChecker;
        $this->translator = $translator;
    }

    public function getFilters()
    {
        return [
            new \Twig_Filter('trans_mail', [$this, 'translate']),
        ];
    }

    /**
     * @param string $translateKey
     * @param string $locale
     *
     * @return string
     */
    public function translate(string $translateKey, string $locale = 'en_EN')
    {
        if ($this->localeChecker->isLocaleExist($locale)) {
            return $this->translator->trans($translateKey, [], 'mail', $locale);
        }

        return $this->translator->trans($translateKey, [], 'mail', $locale);
    }
}