The OT was written in Hebrew, apart from a few passages in the books of Ezra and Daniel which are in Aramaic, the language which predominated in Palestine from the 4th cent. BCE. (Aramaic is another Semitic language closely akin to Hebrew.) With a decline in spoken Hebrew, translations into Aramaic were necessary, and when these had developed into fixed forms, they were then written down and known as targums.
The NT was written in Greek, which was an international language in the Mediterranean basin until it was gradually superseded by Latin by the 6th cent. CE. It is known as koine (‘common’) Greek; a common tongue superseded regional variations, and classical or Attic Greek of the 5th–6th cents. BCE had absorbed words and idioms from the Persian Empire conquered by Alexander the Great. Many papyrus documents discovered in Egypt have thrown light on the meaning of koine Greek words in the NT and the considerable use of the language in 1st‐cent. CE Palestine suggests that Jesus himself may have sometimes spoken it. According to John 19: 20 Pilate put a notice on Jesus' cross in Hebrew, Latin, and Greek.
Latin was spoken by educated people in the western part of the Roman Empire from the 2nd cent. BCE but hardly at all in Palestine; it was the official language in the army and for administration in NT times, but Greek was the main language for communication, and was even used by the Church in Rome for corporate worship until Latin became more widely used by the 3rd cent. CE, and a greater proportion of educated (Latin‐speaking) people had joined the Church. The last Western theologian to write in Greek was Hippolytus (d. 236 CE).
The OT was translated into Greek in Alexandria from the 3rd cent. BCE and so became the scriptures of the early Christians. The NT was translated into Syriac by Tatian in Rome in the middle of the 2nd cent., and into Latin, first in the Roman province of Africa, in the 3rd cent.