'The text you recovered told of a dire champion of Angmar, an Orc of great strength that slew many of my people.
'Is this a legend of old or are these the words of truth? That I cannot say, but this Mordirith's servants are many and powerful...I do not doubt these claims.
'You should investigate the matter. Return to Minas Caul and strike its gates. Should this fabled champion exist, he would be ill-advised to ignore such a challenge.'
Background
Lindir translated the text you found from the Black Speech into Westron.