error_messages_for question

a question about error_messages_for:

when i retrieve the error messages the error_messages_for display a list
errors with the name of input followed the customizable string error.

But if i want to change the name of input on the error message how can i
do?
imagine for example i need to translate the errors messages in various
languages....

You just need to use rails' built-in i18n feature.

Drop a en.yml in config/locales with content like this:

en:
    activerecord:
        models:
            user: "User"
        attributes:
            user:
                login: "user name"
        errors:
            messages:
                blank: 'should not be blank'