You'll find the libretto here: http://www.karadar.com/Librettos/mozart_requiem.html Happy translating!

With the English transalations :) From http://www.geocities.com/amadeusexp/5requiem.html Requiem Diaes Irae Rex tremendae maiestatis Confutatis maledictis Lacrymosa Offertorium Agnus Dei Communion I. Requiem Requiem aeternam dona eis, Domine, et lux perpetua luceat eis. Te decet hymnus, Deus, in Sion, et tibi reddetur votum in Jerusalem. Exaudi orationem meam, ad te omnis care veniet. Requiem aeternam dona eis, Domine, et lux perpetua luceat eis. Kyrie, eleison. Christe, eleison. Kyrie, eleison. I. Requiem Grant them eternal rest, Lord, and let perpetual light shine on them. You are praised, God, in Zion, and homage will be paid to You in Jerusalem. Hear my prayer, to You all flesh will come. Grant them eternal rest, Lord, and let perpetual light shine on them. Lord, have mercy on us. Christ, have mercy on us. Lord, have mercy on us. II. Dies Irae Dies irae, dies illa Solvet saeclum in favilla, teste David cum Sibylla. Quantus tremor est futurus, quando judex est venturus, cuncta stricte discussurus! Tuba mirum spargens sonum, per sepulchra regionum, coget omnes ante thronum. Mors stupebit et natura, cum resurget creatura, iudicanti responsura. Liber scriptus proferetur in quo totum continetur, unde mundus iudicetur. Iudex ergo cum sedebit, quidquid latet, apparebit; nil inultum remanebit. Mors stupebit et natura, cum resurget creatura, iudicanti responsura. Quid sum miser tunc dicturus? Quem patronum rogaturus, cum vix iustus sit securus? II. Dies Irae Day of wrath, day of anger will dissolve the world in ashes, as foretold by David and the Sibyl. Great trembling there will be when the Judge descends from heaven to examine all things closely. The trumpet will send its wondrous sound throughout earth's sepulchres and gather all before the throne. Death and nature will be astounded, when all creation rises again, to answer the judgement. A book will be brought forth, in which all will be written, by which the world will be judged. When the judge takes his place, what is hidden will be revealed, nothing will remain unavenged. Death and nature will be astounded, when all creation rises again, to answer the judgement. What shall a wretch like me say? Who shall intercede for me, when the just ones need mercy? III. Rex tremendae maiestatis Rex tremendae maiestatis, qui salvandos salvas gratis, salva me, fons pietatis. Recordare, Iesu pie, quod sum causa tuae viae: ne me perdas illa die. Quarens me, sedisti lassus: redemisti crucem passus: tantus lagor non sit cassus. Iuste Iudex ultionis, donum fac remissionis ante diem rationis. Ingemisco tamquam reus: culpa rubet vultus meus: supplicanti parce, Deus. Qui Mariam absolvisti, et latronem exaudisti, mihi quoque spem dedisti. Preces meae non sunt dignae: sed tu bonus fac benigne, ne perenni cremer igne. Inter oves locum praesta, et ab haedis me sequestra, statuens in parte dextra. III. Rex tremendae maiestatis King of tremendous majesty, who freely saves those worthy ones, save me, source of mercy. Remember, kind Jesus, my salvation caused your suffering; do not forsake me on that day. Faint and weary you have sought me, redeemed me, suffering on the cross; may such great effort not be in vain. Righteous judge of vengeance, grant me the gift of absolution before the day of retribution. I moan as one who is guilty: owning my shame with a red face; suppliant before you, Lord. You, who absolved Mary, and listened to the thief, give me hope also. My prayers are unworthy, but, good Lord, have mercy, and rescue me from eternal fire. Provide me a place among the sheep, and separate me from the goats, guiding me to Your right hand. IV. Confutatis maledictis Confutatis maledictis, flammis acribus addictis: voca me cum benedictis. Oro supplex et acclinis, cor contritum quasi cinis, gere curam mei finis. IV. Confutatis maledictis When the accused are confounded, and doomed to flames of woe, call me among the blessed. I kneel with submissive heart, my contrition is like ashes, help me in my final condition. V. Lacrymosa Lacrymosa dies illa qua resurget ex favilla iudicantus homo reus. Huic ergo parce, Deus: Pie Iesu Domine, dona eis requiem. Amen. V. Lacrymosa That day of tears and mourning, when from the ashes shall arise, all humanity to be judged. Spare us by your mercy, Lord, gentle Lord Jesus, grant them eternal rest. Amen. VI. Offertorium Domine Iesu Christe, Rex gloriae, libera animas omnium fidelium defunctorum de poenis infernis et de profundu lacu: libera eas de ore leonis; ne absorbeat eas tartarus, ne cadant in obscurum. Sed signifer sanctus Michael repraesentet eas in lucem sanctam. Quam olim Abrahae promisisti et semini eius. Hostias et preces tibi, Domine, laudis offerimus: tu suscipe pro animabus illis, quarum hodie memoriam facimus. Fac eas, Domine, de morte transire ad vitam. VI. Offertorium Lord Jesus Christ, King of glory, liberate the souls of the faithful, departed from the pains of hell and from the bottomless pit. Deliver them from the lion's mouth, lest hell swallow them up, lest they fall into darkness. Let the standard-bearer, holy Michael, bring them into holy light. Which was promised to Abraham and his descendants. Sacrifices and prayers of praise, Lord, we offer to You. Receive them in behalf of those souls we commemorate today. And let them, Lord, pass from death to life VII. Agnus Dei Agnus Dei, qui tollis peccata mundi, dona eis requiem. Agnus Dei, qui tollis peccata mundi, dona eis requiem. Agnus Dei, qui tollis peccata mundi, dona eis requiem sempiternam. VII. Agnus Dei Lamb of God, who takes away the sins of the world, grant them eternal rest. Lamb of God, who takes away the sins of the world, Grant them eternal rest. Lamb of God, who takes away the sins of the world, grant them eternal rest forever. VII. Communion Lux aeterna luceat eis, Domine, cum sanctis tuis in aeternum, quia pius es. Requiem aeternum dona eis, Domine, et Lux perpetua luceat eis, cum Sanctus tuis in aeternum, quia pius es. VII. Communion Let eternal light shine on them, Lord, as with Your saints in eternity, because You are merciful. Grant them eternal rest, Lord, and let perpetual light shine on them, as with Your saints in eternity, because You are merciful

The text of Mozart's Requiem is, of course, by no means unique. It is the standard funeral mass text of the Roman Catholic Church. The authoritative source of the text of the Requiem mass, then, would be the Liber Usualis (the "Usual Book"), a collection of all of the Roman Catholic mass texts and the plainchant tunes associated with them, as authorized by that church, itself. This book is published by St. Bonaventure Publications, and would be available in any good library.