Description:
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mb_convert_encoding supports a charset known as "shift-jis", an old japanese character set, but it seems to be undocumented.. also my only test data is a bunch of vulgar japanese text, sorry about that :/ ... i don't understand/write/speak japanese myself

Test script:
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<?php 
$str=base64_decode("g2+DQ4N1g4yBW4NegVuCxZbjgqaCxIKigumOcILwinmCtYLegsiC8YLE");
var_dump(mb_convert_encoding($str,'utf-8','shift-jis'));