There are actually two separate questions here, which need to be clarified.
In what form was the original Rosary of the Blessed Virgin Mary?
What was the form of the original Hail Mary?
First of all let us deal with the Hail Mary. And in order to understand the origins of this prayer we basically need to see this in the light of the Church's liturgical and official language: Latin, since vernacular languages will vary considerably.
Ave Maria, gratia plena, Dominus tecum.
Benedicta tu in mulieribus, et benedictus fructus ventris tui, Iesus.
Sancta Maria, Mater Dei, ora pro nobis peccatoribus, nunc et in hora mortis nostrae.
Let's start with the origins of the Ave Maria and who added the later portions of this wonderful prayer.
Although Wikipedia states that Saint Peter Canisius (1521-1597 , a Doctor of the Church is credited with adding to the Hail Mary the sentence "Holy Mary, Mother of God, pray for us sinners", seems to be doubtful. It is plausible that St Peter Canisius had some influence at the Council of Trent in rendering the Hail Mary as we know it in its' official form.
Who wrote the Hail Mary prayer?
Actually, we owe the first half of it to the angel Gabriel and to Mary’s cousin Elizabeth. “Hail, full of grace, the Lord is with thee,” are the words of the angel when he greets Mary at the Annunciation (Luke 1:28). During the visitation, Mary’s cousin Elizabeth welcomes her with the words, “Blessed are you among women, and blessed is the fruit of your womb.” (Luke 1:42). The joining of the two salutations in prayer appears to have become a widespread practice in the mid-eleventh century, though there is evidence of it showing up in eastern rites as far back as the sixth century.
The second part of the “Hail Mary” is where we ask for Mary’s intercession: “Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death.” Various forms of this go back to the fourteenth century; the wording as we use it today became official in 1568.
The devotion to the hail Mary can be traced at least to the 11th century, at least as Marian Salutation.
Abbot Baldwin, the Archbishop of Canterbury in 1184 wrote about a devotion to the ‘Hail Mary’ prayer and said, “To this salutation of the Angel, by which we daily greet the most Blessed Virgin, with such devotion as we may, we are accustomed to add the words, “and blessed is the fruit of thy womb,” by which clause Elizabeth at a later time, on hearing the Virgin’s salutation to her, caught up and completed, as it were, the Angel’s words, saying: “Blessed are thou amongst women and blessed is the fruit of thy womb.” - 11 Historical Facts You Probably Didn’t Know about the Hail Mary, but Should
The Hail Mary as we know it can be found in books from the 1400s.
Dominican reformer Girolamo Savonarola wrote a piece in 1495 that contained the entire Hail Mary except the word ‘nostrae.’ There is currently a copy of this work in the British Museum. - 11 Historical Facts You Probably Didn’t Know about the Hail Mary, but Should
The Catholic Encyclopedia states something quite similar:
We meet the Ave as we know it now, printed in the breviary of the Camaldolese monks, and in that of the Order de Mercede c. 1514. Probably this, the current form of Ave, came from Italy, and Esser asserts that it is to be found written exactly as we say it now in the handwriting of St. Antoninus of Florence who died in 1459. This, however, is doubtful. What is certain is that an Ave Maria identical with our own, except for the omission of the single word nostrae, stands printed at the head of the little work of Savonarola's issued in 1495, of which there is a copy in the British Museum. Even earlier than this, in a French edition of the "Calendar of Shepherds" which appeared in 1493, a third part is added to the Hail Mary, which is repeated in Pynson's English translation a few years later in the form: "Holy Mary moder of God praye for us synners. Amen.". In an illustration which appears in the same book, the pope and the whole Church are depicted kneeling before our Lady and greeting her with this third part of the Ave. The official recognition of the Ave Maria in its complete form, though foreshadowed in the words of the Catechism of the Council of Trent, as quoted at the beginning of this article, was finally given in the Roman Breviary of 1568.
The Hail Mary in the recitation of the Most Holy Rosary in our modern times has the ending as such is in English "Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death" or as in French "Sainte Marie, Mère de Dieu, priez pour nous, pauvres pécheurs, maintenant et à l'heure de notre mort" did not exist when the original rosary was thought to have been composed.
Seeing that in the early development of the rosary, it was a more scriptural way of meditating on the sacred mysteries of the life of Our Lord, since the original Hail Mary comprise of two elements the angelic salutation of the Angel Gabriel (Luke 1:28) and St Elizabeth's words at Mary's Visitation (Luke 1:42).
Traditionally, the origins of the Holy rosary itself are believed to have been handed down from St Dominic in the year 1214. This may or may not be true.
According to some Catholic traditions, the Rosary was given to Saint Dominic in a vision of the Blessed Virgin Mary and it was then promoted by Blessed Allan de la Roche. However, not all Catholics agree with that tradition. Some historians see a more gradual development for the Rosary, in that the repetition of Marian prayers which form the basis of the Rosary needed counting devices, which resulted in the modern form of the Rosary prayed on beads. - Wikipedia
The Catholic Encyclopedia has a more reserved approach to its' origin as a whole and tends to see the rosary as a natural development of piety:
We have positive evidence that both the invention of the beads as a counting apparatus and also the practice of repeating a hundred and fifty Aves cannot be due to St. Dominic, because they are both notably older than his time. Further, we are assured that the meditating upon the mysteries was not introduced until two hundred years after his death. What then, we are compelled to ask, is there left of which St. Dominic may be called the author?
These positive reasons for distrusting the current tradition might in a measure be ignored as archaeological refinements, if there were any satisfactory evidence to show that St. Dominic had identified himself with the pre-existing Rosary and become its apostle. But here we are met with absolute silence. Of the eight or nine early Lives of the saint, not one makes the faintest allusion to the Rosary. The witnesses who gave evidence in the cause of his canonization are equally reticent. In the great collection of documents accumulated by Fathers Balme and Lelaidier, O.P., in their "Cartulaire de St. Dominique" the question is studiously ignored. The early constitutions of the different provinces of the order have been examined, and many of them printed, but no one has found any reference to this devotion.