fix content error translation when content_name is nested on element

 I have content names translations in this way:

```yaml
es:
  alchemy:
    content_names:
      contactform:
        mail_from: Remitente
        mail_to: Enviar aviso a
        subject: Asunto
        success_page: Página de éxito
```

They are translated on editor, but not in error messages