It is possible to standardize the error messages used in DataAnnotations, so that you do not have to pass a string like:
[Required(ErrorMessage = "Este campo é obrigatório.")]
But you can use more or less like this:
string mensagem = "Este campo é obrigatório.";
[Required(ErrorMessege = mensagem)]
Yes, use a Resource for this. In my case it's called Error.resx:
[Required(ErrorMessageResourceName = "CampoObrigatorio", ErrorMessageResourceType = typeof(MensagemErro))]
Basically I say that I have a resource of type MensagemErro with a name called CampoObrigatorio .
In my example I still use a {0} to concatenate a name, but ignore it in your case.