respect-validation/docs/message-translation.md

Message translation

You're also able to translate your message to another language with Validation. The only thing one must do is to define the param translator as a callable that will handle the translation overwriting the default factory:

Factory::setDefaultInstance(
    (new Factory())->withTranslator('gettext')
);

The example above uses gettext() but you can use any other callable value, like [$translator, 'trans'] or you_custom_function().

After that, if you call getMessage(), getMessages(), or getFullMessage(), the message will be translated.