The Septuagint is the Old Testament in Greek translated by 70 Jewish scholars. ‘Septuagint’ or ‘LXX’ means ‘70’. It was written in the 3rd century BC and may have been commissioned by Ptolemy II Philadelphus (285-247 BC) to put in the library in Alexandria. It was used by Alexandrian Jews living in Egypt.
The Septuagint was translated from Hebrew into Greek from the Hebrew Bible with the Hebrew canon of scripture. In addition to this, mainstream books used by rabbis were included in the appropriate locations in between the other books. These additional books are now known as the Apocrypha or ‘hidden books’.
The later books of the Apocrypha such as Maccabees and Sirach were added to the Septuagint Bible in the 2nd century BC. Thus, there was more than one version of the Septuagint.
During the Second Temple era most Jews could not read Hebrew so they read the Bible in Greek. The Septuagint written in Greek was in widespread use among Hellenized Jews.
The apostles and other Christians, both Jews and gentiles, read the Septuagint Bible. St Paul’s letters quote the Septuagint Bible. This implies that Jesus approved of the Bible in Greek with all of the canonical and non-canonical books in it. Jesus himself would have read the Greek Bible.
It was natural that Orthodox Christians who were Greek-speaking adopt the Septuagint as the basis to their Christian Bible. The Septuagint was the basis for Armenian, Coptic, Syriac and Slavonic Bibles. The Catholics followed suit and also included all of these Apocryphal books when they translated the Bible into Latin.
Most of the church fathers knew the Bible from the Greek versions of it. St Augustine promoted the Septuagint Bible when St Jerome started to compile his Latin Vulgate Bible by translating the Hebrew Bible into Latin. St Jerome wanted to leave out the books written in Greek, but was persuaded to put them in.
The Jews who were exiled after the destruction of the Second Temple found themselves as rivals to Christians in a new Christian world. These exiled Jews wanted to distinguish themselves from Christians and show that they had the more authentic tradition. For this reason they reverted from the Septuagint Bible in Greek to the Hebrew Bible in Hebrew called the Tanakh with the books of Moses called the Torah.
At the Reformation, Protestant reformers were seeking to throw off all the overlays that were obscuring the Christian faith under Catholicism with its centuries of church traditions. One major thing they did was to translate the Bible into the language of the people from the Hebrew. They adopted the Hebrew Bible canon of scripture which excluded the Apocryphal books. Thus, Protestant Bibles in English, German or French etc have less books than Orthodox and Catholic Bibles.
Orthodox and Catholic Bibles have now been translated into languages other than Greek and Latin, but they retain the additional books of the Septuagint Bible in varying numbers.
One Protestant Bible, the King James Bible written in quaint old English, retains the Apocrypha but as a separate section.