UNICODE is not an encoding, at least not on its own. It assigns numbers to characters, but it doesn't dictate how those numbers are represented as bytes. Encodings UTF-8, UTF-16, etc provide this missing information. You'll need to fix the header with the proper encoding. If the file actually uses the UTF-8 enconding you could do use something like the following to fix the file:

$xml =~ s/encoding="(?i:UNICODE)"/encoding="UTF-8"/;
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