Most of the Old Testament was written in Hebrew, that is, the language of the Israelites.
There are a few places in the Old Testament where a different language was used. This language is called Aramaic. The Aramaic language was used in Genesis 31:47; Jeremiah 10:11; Daniel 2:4-7:28; Ezra 4:8-6:18, 7:12-26. The Jews started speaking Aramaic during the time of the Babylonian exile. Aramaic was similar to the Hebrew language.
About 300 years before Jesus was born, the Old Testament was translated into Greek. This translation is sometimes called “the Greek Old Testament” or the “Septuagint.”