You need to convert the "%HH" strings to their binary byte values, then "decode" (actually, just flag) the string as containing utf8 data -- something like this:

use Encode;

# ...
# assuming the source string is in $_:

s/%([0-9A-F]{2})/chr(hex($1))/egi;  # convert "%HH" to binary bytes

$_ = decode( 'utf8', $_ );  # flag the string as utf8 data
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(BTW, you seem to be right, the intent of the original text is to convey utf8 characters -- in this case, by converting each byte of each "wide" utf8 character as a sequence of hex byte values prefixed by "%".)