Yes indeed it should be UTF-8 but we've already established that the file has "strange" (being polite) encoding...

$| = 1;
$/ = undef;
print "Reading JSON file";
open my $fh, '<:encoding(UTF-8)', '../data/publicextract.charity.json'
+ or die "Unable to read Charity JSON File";
my $data = <$fh>;
close $fh;
print "...done\n";

$data =~ s/^\x{feff}//;  # Strip off BOM

print "Decoding JSON file";
my $js = decode_json $data;  # line 24
print "...done\n";
[download]

This takes about 10 minutes to read the 462Mb JSON file then fails with Decoding JSON fileWide character in subroutine entry at import.pl line 24

Given the time taken to open the file in UTF-8 and the error, I am thinking there is some nasty encoding hidden somewhere in this file

UPDATE

Changing the encoding like so

print "Reading JSON file";
open my $fh, '<', '../data/publicextract.charity.json' or die "Unable 
+to read Charity JSON File";
my $data = <$fh>;
close $fh;
print "...done\n";

$data =~ s/^\357\273\277//;  # Strip off BOM
[download]

"Strange" because the error doesn't include at import.pl line 24!

Another UPDATE

It seems I might be running out of memory...380400 records in the JSON file seems to be too much...

unfortunately° are - like already said - decode_json and encode_json defaulting to utf8-encoded octet-streams

you need to use the object interface

use v5.12;
use warnings;
use Devel::Peek;
use Data::Dump qw/pp/;
use JSON::XS;
use utf8;

my $str = "\x{feff}"
  . '["whät","över"]';                  # Internal Unicode b/c of use 
+utf8

Dump($str);                             # hence shows UTF8 flag

$str =~ s/^\x{feff}//;                  # strip BOM by Unicode code-po
+int

Dump($str);                             # shows UTF8 flag

my $JSON = JSON::XS->new;               # coder for all unicode in/out

my $data = $JSON->decode($str);

warn pp '$data: ', $data;               # ["wh\xE4t", "\xF6ver"]
                                        # NB: \xE4, \xF6 correct codep
+oints for umlauts 
                                        # even if each character neede
+d 2 bytes

my $str2 = $JSON->encode($data);        # roundtrip

Dump($str2);                            # shows UTF8 flag

warn '$str eq $str2: ', $str eq $str2;  # same
[download]

    
SV = PV(0x6bcea8) at 0x26485f0
  REFCNT = 1
  FLAGS = (POK,pPOK,UTF8)
  PV = 0x28229e8 "\357\273\277[\"wh\303\244t\",\"\303\266ver\"]"\0 [UT
+F8 "\x{feff}["wh\x{e4}t","\x{f6}ver"]"]
  CUR = 20
  LEN = 22
SV = PV(0x6bcea8) at 0x26485f0
  REFCNT = 1
  FLAGS = (POK,pPOK,UTF8)
  PV = 0x28227e8 "[\"wh\303\244t\",\"\303\266ver\"]"\0 [UTF8 "["wh\x{e
+4}t","\x{f6}ver"]"]
  CUR = 17
  LEN = 24
("\$data: ", ["wh\xE4t", "\xF6ver"]) at d:/perl/pm/t_devel_peek.pl lin
+e 21.
SV = PV(0x6bd158) at 0x27482a0
  REFCNT = 1
  FLAGS = (POK,pPOK,UTF8)
  PV = 0x281d9c8 "[\"wh\303\244t\",\"\303\266ver\"]"\0 [UTF8 "["wh\x{e
+4}t","\x{f6}ver"]"]
  CUR = 17
  LEN = 66
$str eq $str2: 1 at d:/perl/pm/t_devel_peek.pl line 28.
[download]

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)
Wikisyntax for the Monastery}

°) or fortunately? depends on the perspective