[Validator] Add a section for custom translation domain

Author: HeahDude

validation/translations.rst

@@ -135,5 +135,65 @@ Now, create a ``validators`` catalog file in the ``translations/`` directory:
             'author.name.not_blank' => 'Please enter an author name.',
         ];
 
-You may need to clear your cache (even in the dev environment) after creating this
-file for the first time.
+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:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/packages/translation.yaml
+        framework:
+            translator:
+                translation_domain: validation_errors
+
+    .. code-block:: xml
+
+        <!-- config/packages/translation.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <container xmlns="http://symfony.com/schema/dic/services"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xmlns:framework="http://symfony.com/schema/dic/symfony"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services
+                https://symfony.com/schema/dic/services/services-1.0.xsd
+                http://symfony.com/schema/dic/symfony
+                https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
+
+            <framework:config>
+                <framework:translator
+                    translation-domain="validation_errors"
+                />
+            </framework:config>
+        </container>
+
+    .. code-block:: php
+
+        // config/packages/translation.php
+        use Symfony\Config\FrameworkConfig;
+
+        return static function (FrameworkConfig $framework) {
+            // ...
+            $framework
+                ->defaultLocale('en')
+                ->translator()
+                    ->translationDomain('validation_errors')
+            ;
+        };
+
+Or it can be customized for a specific violation from a constraint validator::
+
+    public function validate($value, Constraint $constraint): void
+    {
+        // validation logic
+
+        $this->context->buildViolation($constraint->message)
+            ->setParameter('{{ string }}', $value)
+            ->setTranslationDomain('validation_errors')
+            ->addViolation();
+    }