From what I understand it is still in contention whether aramaic formed a lot of the original language. While spoken by many, it is thought that greek and hebrew formed most of the writings.
To make it simple, Hebrew and Aramaic are close enough to the same thing that they can be treated as such by those of us who can't read or speak them. The OT is written in Hebrew and Aramaic. If I understand correctly, Aramaic is basically Hebrew with Chaldean (Babylonian) influence brought in after the captivity there. There's no language controversy about the OT.
The NT was written in Greek (very likely, in my opinion), and there is controversy over whether the originals were written in Aramaic. By then, Hebrew had become Aramaic, so it is only the NT that is in controversy. I think people like Brian, who study such things, would say that it's possible Matthew or Q were written in Aramaic, but it's unlikely much else in the NT was. The rest would be Greek.
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