nl: default_error_messages is a dictionary with 4 initial entries: return value of the function _ called with string as an argument,
code: default_error_messages = { 'invalid' : _ ( 'Enter a number.' ) , 'max_digits' : ungettext_lazy ( 'Ensure that there are no more than %(max)s digit in total.' , 'Ensure that there are no more than %(max)s digits in total.' , 'max' ) , 'max_decimal_places' : ungettext_lazy ( 'Ensure that there are no more than %(max)s decimal place.' , 'Ensure that there are no more than %(max)s decimal places.' , 'max' ) , 'max_whole_digits' : ungettext_lazy ( 'Ensure that there are no more than %(max)s digit before the decimal point.' , 'Ensure that there are no more than %(max)s digits before the decimal point.' , 'max' ) , }