How to Translate Validation Constraint Messages

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The validation constraints used in forms can translate their error messages by creating a translation resource for the validators translation domain.

First of all, install the Symfony translation component (if it's not already installed in your application) running the following command:

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$ composer require symfony/translation

Suppose you've created a plain-old-PHP object that you need to use somewhere in your application:

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// src/Entity/Author.php
namespace App\Entity;

class Author
{
    public $name;
}

Add constraints through any of the supported methods. Set the message option to the translation source text. For example, to guarantee that the $name property is not empty, add the following:

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// src/Entity/Author.php
namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;

class Author
{
    /**
     * @Assert\NotBlank(message="author.name.not_blank")
     */
    public $name;
}

Now, create a validators catalog file in the translations/ directory:

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<!-- translations/validators/validators.en.xlf -->
<?xml version="1.0" encoding="UTF-8" ?>
<xliff version="1.2" xmlns="urn:oasis:names:tc:xliff:document:1.2">
    <file source-language="en" datatype="plaintext" original="file.ext">
        <body>
            <trans-unit id="author.name.not_blank">
                <source>author.name.not_blank</source>
                <target>Please enter an author name.</target>
            </trans-unit>
        </body>
    </file>
</xliff>

You may need to clear your cache (even in the dev environment) after creating this file for the first time.

Custom Translation Domain

The default translation domain can be changed globally using the FrameworkBundle configuration:

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# config/packages/validator.yaml
framework:
    validation:
        translation_domain: validation_errors

Or it can be customized for a specific violation from a constraint validator:

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public function validate($value, Constraint $constraint): void
{
    // validation logic

    $this->context->buildViolation($constraint->message)
        ->setParameter('{{ string }}', $value)
        ->setTranslationDomain('validation_errors')
        ->addViolation();
}
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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