Here is my attempt at a decent translation of Parce, Domine which retains the melody of the Latin chant.
R. Spare Thy people, Lord; spare us, Lord, we kneel here before Thee: lest Thy anger stay upon us forever.
1. To our knees we fall before Thy wrath, weeping tears of true contrition; crying out in supplication, we call to Thee with sorrowful hearts.
2. By our sins we have offended Thee, transgressing upon Thy mercy; pour down upon us from on high Thy gracious pardon, merciful One.
3. Cleanse the off'ring of our hearts, O Lord, in our tears and Thy charity: now is the day of salvation, now is a most acceptable time.
4. O benign Creator hear our prayers, bend Thine ear to our lamentations, in this season of penitence, this holy Lent of forty days.
5. O, beloved searcher of the heart, Thou Who knowest ev'ry weakness; grant Thy grace of forgiveness to those returning unto Thee.