I think Augustine considered Wisdom a part of the Old Testament. I don't think anyone considers it, or any of the deuterocanonical works, part of the New Testament. Open a Douhay-Rheims (Catholic) Bible and you'll find it towards the end of the Old Testament. Protestants don't have it in their Bibles, since Luther (I believe) removed it (as if he had such authority).
Most Protestants today simply inherited Luther's error, without being privy to it. Most, I'm sure, are unaware the deuterocanonical books exist.
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