I've found two sources online for the Latin text, but unfortunately nothing in English. The Latin is available in Gousset's Les actes de la province ecclésiastique de Reims, page 233, as well as Hefele's Conciliengeschichte, volume IV, page 187. The first of these includes a very brief introduction in French, while the second has more extensive commentary in German. The Catechism's quote comes from this phrase:
Christus Jesus Dominus noster, sicut nullus homo est, fuit, vel erit, cujus natura in illo assumpta non fuerit, ita nullus est, fuit, vel erit homo, pro quo passus no fuerit
As far as English goes, the best online version I have found is Schaff's paraphrase and commentary in his History of the Christian Church:
Hincmar secured the confirmation of his views by the Synod of Chiersy, held in presence of the Emperor, Charles the Bald, 853, It adopted four propositions:
- God Almighty made man free from sin, endowed him with reason and the liberty of choice, and placed him in Paradise. Man, by the abuse of this liberty, sinned, and the whole race became a mass of perdition. Out of this massa perditionis God elected those whom he by grace predestinated unto life eternal; others he left by a just judgment in the mass of perdition, foreknowing that they would perish, but not foreordaining them to perdition, though he foreordained eternal punishment for them. This is Augustinian, but weakened in the last clause.
- We lost the freedom of will through the fall of the first man, and regained it again through Christ. This chapter, however, is so vaguely worded that it may be understood in a Semi-Pelagian as well as in an Augustinian sense.
- God Almighty would have all men without exception to be saved, although not all are actually saved. Salvation is a free gift of grace; perdition is the desert of those who persist in sin.
- Jesus Christ died for all men past, present and future, though not all are redeemed by the mystery of his passion, owing to their unbelief.
A more direct translation may be available in Gottschalk and a Medieval Predestination Controversy, based on the book's description, but I haven't been able to confirm that these four propositions are included.