The Old Testament is written primarily in Hebrew. It is commonly known as Biblical Hebrew because it is different from Modern Hebrew, just as Old English is different from Modern English. Because the time span from Genesis to Malachi is so great, there is even evidence of development within the language during that time span. Biblical Hebrew was similar to the languages spoken by other peoples in the region at that time, and sometimes literature from the surrounding areas helps us understand the meaning of an ancient Hebrew word.
Aramaic was the language of the Babylonian Empire, and as the Jews were exiled to Babylon, many of them started to use that language. Some portions of the book of Daniel were written in Aramaic. This might be expected, as Daniel was an exile in Babylon. In the book of Ezra, there are transcriptions of several Babylonian court documents that were also written in Aramaic.
During what is known as the intertestamental period, the 400 years between the prophet Malachi and the birth of Christ, Greek became the language of the “civilized world” primarily due to the conquests of Alexander the Great. During this time, the Old Testament was translated into Greek, a translation known as the Septuagint (often abbreviated as LXX). The word Septuagint comes from the word for “seventy” because it was reported that seventy scholars worked on the translation—thus the Roman numeral LXX. When the Old Testament is quoted in the New Testament, the majority of the quotations are taken from the LXX rather than the Hebrew Bible. Most Gentile converts would have been unable to read Hebrew, but they would have had much more access to the LXX.
During Jesus’ time on earth, Aramaic was the language spoken in Israel. However, the gospels were written in Greek. Therefore, with only a few exceptions (Mark 5:41, Mark 7:34, and Matthew 27:46), the New Testament does not contain the exact words of Jesus—it contains an accurate Greek translation of them.
The New Testament was written in Koine Greek, often simply referred to as Koine. Koine means “common.” It was not the formal, academic Classical Greek used by scholars of the day. It was the language of the common people. If it were not for the New Testament, there would be no study of Koine Greek today, simply because Koine was not used for important literary works. As is often the case, God chose to exalt that which was lowly—the Koine language—to the most important place of all.
Some New Testament authors wrote in a complex, beautiful style (Luke), and others give evidence that Greek was not their first language (Peter), but they all wrote in Koine Greek, the language of the commoners.
Since the time the Bible was written, portions of it have been translated into thousands of languages. An accurate translation is just as much the Word of God as the original. However, if a person wants to become a serious student of the Word of God, some knowledge of Koine Greek and Biblical Hebrew will be very helpful.