sub convert {
    my ($s) = @_;
    $s =~ s/&#x([[:xdigit:]]{4});/\\u$1/gr
}

my $entities_json = '{"school":"Eötvös Loránd University"}';
my $converted_json = convert($entities_json);

print "Original JSON: [$entities_json]\n";
print "Converted JSON: [$converted_json]\n";  # [{"school":"E\u00F6tv\u00F6s Lor\u00E1nd University"}]

my $decoded_json = decode_json($converted_json);

binmode STDOUT, ':encoding(UTF-8)';
print "School: " . $decoded_json->{'school'} . "\n";  # Eötvös Loránd University