In what language was the Gutenberg Bible printed?
Latin, or more accurately what is termed "Latin vulgate." The term means today the Latin version of the Holy Bible (or "Separated Book", ie the book separate or different from all other books), prepared largely by Jerome in the 5th Century. The term comes from vulgata editio and originally meant "current or regularly used text." Verseo vulgata became the term for this translation as time went on, in usage meaning "common translation." The term vulgate later was used to also refer to other Latin texts, such as the University of Paris' version of the Arthurian tales, etc.
Johann Gutenberg was born in Mainz about 1400, moved to Strasbourg and was later a printer, again in his native city. He invented the first mechanical printing process, which he may have been experimenting with as early as the late 1440s. In 1455 Enea Piccolomini wrote that he had seen portions of a printed Bible. This letter by the future Pope Pius II is the first mention of the Gutenberg Bible, the first printed book in history.
The vulgate text was the result of a commission by Pope Damascus I in 382, who asked Jerome (Eusebius Sophronius Hieronymus) to make a translation of the four gospels. Two years later, when the pope died, he had completed these plus much of the Psalms and some other parts of the New Testament. St. Jerome, who was also a noted critic of the secular (non-closeted) priesthood, had many enemies in Rome, and was without protection from them following the death of his patron. The following year he left Rome for Bethleham, where he lived the remainder of his life. Dying in 420, he spent these years finishing his translation of the Bible, plus many other writings including a catalogue of Christian writers and commentaries on the Biblical texts.