Lex Mahumet pseudoprophete
Lex Mahumet pseudoprophete (English: "Law of Muhammad the false prophet") is the translation of the Qur'an into Latin by Robert of Ketton (c.1110-1160). It is the earliest translation of the Qur'an into a Western language.
In 1142 Peter the Venerable persuaded Robert to join a team he was creating to translate Arabic works into Latin in hopes of aiding the religious conversion of Muslims to Christianity. The principal work of this collection was to translate the Qur'an, Islam's revealed law. The undertaking was huge, taking over a year and filling over 100 folios (180 pages in modern print). This translation of the Qur'an was popular in its time, with over 25 manuscripts still existing, together with two 16th century prints. It was the standard translation for Europeans from its release until the 18th century.
Despite its success and early influence, scholarly consensus deems the text unreliable. Thomas E. Burman states, "from the 15th century to the present, scholarly opinion has condemned it as a loose, misleading paraphrase". Juan de Segovia criticised the translation for the liberties Robert of Ketton took with it. The traditional 114 suras had been expanded into more, and Juan de Segovia claimed that the explicit from the Arabic was often left out while the implicit was included, not to mention numerous order changes. Ludovico Marracci, Hadrian Reland, and George Sale all criticized the translation with Sale even stating that it "deserve[d] not the name of a translation".
Muslim-Christian relations 
Peter the Venerable's explicit purpose for commissioning the translation was the conversion of Muslims and so the project can be criticised as inherently hostile to Islam. Catholics (see also the translation by Mark of Toledo) were translating the works of an opposing or competing religion. Many[who?] theorize the reason for the subpar standard of early translations was the unwillingness of Medieval Latin translators (because of Christendom's hostility towards the Muslim world) to turn towards authoritative Muslim sources when attempting to decipher difficult parts of the text. This notion is being chipped away by scholars such as Thomas Burman, as they try to show use of tafsir (exegesis) in furthering the translation by Robert of Ketton in Lex Mahumet pseudoprophete and similar, later endeavors by Mark of Toledo. Burman believes that the use of tafsir shows a willingness on the part of some Latin translators to trust what Muslims said about their religious book and in a broader scope, to try to look objectively on Islam as a whole.
Sample texts 
INCIPIT LEX SARACENORUM, QUAM ALCORAN VOCANT, ID EST, collectionem praeceptorum.
Misericordi pioque Deo, universitatis creatori, iudicium cuius postremo die expectat(ur), voto simplici nos humiliemus, adorantes ipsum sueque manus suffragium semiteque donum et dogma qua suos ad se benivolos nequaquam hostes et erroneos adduxit, iugiter sentiamus.
How can ye reject the faith in Allah?- seeing that ye were without life, and He gave you life; then will He cause you to die, and will again bring you to life; and again to Him will ye return. *
Hic namque uos ad uitam de non esse deducens mortem inducet et ad se uos resurgere faciet
For he, drawing you out of nonbeing into life, will bring on death, and will make you rise up to him.
Qualiter blasphematis in Deum? Et eratis mortui, [et] uiuificauit uos; deinde mortificabit uos; deinde uiuificabit; demum ad eum redibitis.
How can you disbelieve in God? For when you were dead, he gave you life, and then he will cause you to die, and then he will give you life, and then to him you will be returned.
This example shows the tendency of Robert of Ketton's translation to rework the original structure of the Qur'an compared to the very literal interpretation of his contemporary Mark of Toledo. Both of these can be compared to the widely accepted modern translation in order to show the differences between modern and Medieval translation practices. With Burman's translation of a translation some meaning of the original text may be lost.
See also 
- Thomas E. Burman. Tafsir and Translation: Traditional Arabic Quran Exegesis and the Latin Qurans of Robert of Ketton and Mark of Toledo. Speculum, Vol. 73, No. 3. (Jul., 1998), pp. 703-732. <Stable URL>
- Burman., 705
- Burman., 706
- Marie-Thérèse D'Alverny, "Motives and Circumstances, Methods and Techniques of Translation from Arabic to Latin," Colloquium on the Transmission and Reception of Knowledge, Dumbarton Oaks, 5-7 May 1977, Washington, D.C. 
- Burman., 709
- The latin Qu'ran, as edited by Bibliander (1550 revised edition, complete text online)