There are loads of websites with Archangl St. Michael prayers and therefore our task was to present the 'correct' prayer. After quite some research, we found the longer version in the Raccolta, edition 1903 and decided that we use that one.
The standard St. Michael the Archangel prayer is both in English and in Latin. The authentic long version longer prayer to St Michael the Archangel is only in English.
Prayer to Archangel St. Michael
Saint Michael the Archangel, defend us in battle. Be our protection against the wickedness and snares of the devil. May God rebuke him, we humbly pray; and do Thou, O Prince of the Heavenly Host - by the Divine Power of God - cast into hell, satan and all the evil spirits, who roam throughout the world seeking the ruin of souls.
Sancte Michael Archángele,
defénde nos in prœlio;
contra nequítiam et insídias diáboli esto præsídium.
Imperet illi Deus, súpplices deprecámur;
tuque, Princeps militiae cæléstis, Sátanam aliósque spíritus malignos,
qui ad perditiónem animárum pervagántur in mundo,
divina virtúte in inférnum detrúde.
Prayer to St Michael the Archangel
(authentic long version)
Raccolta 1903, p. 364-366, Pope Leo XIII (1888)
Most glorious prince of the heavenly hosts, Archangel St. Michael, defend us in the battle and in the tremendous struggle we carry on against the Principalities and Powers, against the rulers of the world of darkness and all evil spirits. Come to the help of man, whom God created immortal, fashioned to his own image and likeness, and rescued at a great price from the tyranny of the devil. With the great army of the holy angels fight to-day the battle of the Lord as thou didst of old fight against Lucifer, the leader of the proud, and his apostate angels, who were powerless against thee, and they had no longer a place in heaven ; and that monster/ the old serpent who is called the devil and Satan, that seduces the whole world, was cast into hell with his angels. But now that first enemy and homicide has regained his insolent boldness. Taking on the appearance of an angel of light, he has invaded the earth, and, with his whole train of evil spirits, he is prowling about among men, striving to blot out the name of God and of his Christ, to capture, to destroy, to drag to eternal perdition the souls destined to the crown of eternal glory. That malignant dragon is pouring abroad, like a foul stream, into the souls of men of ruined intellect and corrupt heart the poison of his wickedness, the spirit of lying, of impiety and blasphemy, the pestilent breath of impurity and of all vice and iniquity. Most cunning enemies have filled with bitterness and drenched with gall the Church, the Spouse of the Lamb without spot, and have lifted impious hands against all that is most sacred in it. Even in the holy place where the See of Blessed Peter and the chair of truth was set up to enlighten the world, they have raised the abominable throne of their impiety with the iniquitous hope that the Shepherd may be stricken and the flock scattered abroad.
Arise, then, unconquerable Prince, defend the people of God against the assaults of the reprobate spirits, and give them the victory. Holy Church reveres thee as its guardian and patron ; it glories in thee as its defender against the malignant powers of hell ; to thee God has committed the souls that are to be conveyed to the seats of the Blessed in eternal happiness. Pray, then, to the God of peace, that he may put Satan under our feet, so completely vanquished that he may no longer be able to hold men in bondage and work harm to the Church. Offer up our prayers before the Most High, so that the mercies of the Lord may prevent us, and lay hold of the dragon, the old serpent, who is the devil and Satan, and hurl him bound in chains into the abyss where he may no longer seduce the souls of men.
V. Behold the Cross of the Lord, fly ye hostile ranks.
R. The Lion of the tribe of Juda, the Root of David, has conquered.
V. May thy mercies, O Lord, be fulfilled in us.
R. As we have hoped in thee.
V. Lord, hear my prayer.
R. And let my cry come unto thee.
Let us pray
O God, and the Father of our Lord Jesus Christ, we call upon thy holy name and humbly beseech thy clemency, that, through the intercession of the ever immaculate Virgin and our Mother Mary, and of the glorious Archangel Saint Michael, thou wouldst vouchsafe to help us against Satan and all the other unclean spirits that are prowling about the world to the great peril of the human race and the loss of souls.
His Holiness, Leo XIII., Motu Proprio, September 25, 1888,
granted to the faithful who recite the above prayer