use warnings;
use strict;
use Data::Dumper;
use JSON::PP qw/decode_json/;

my $json = <<'JSON';
{
	"myData" : [
		{ "Lang4":"ok", "Lang9":"well", "Lang7":null, "Lang6":null },
		{ "Lang4":"one", "Lang9":"two", "Lang7":null, "Lang6":null }
	]
}
JSON

my $data = decode_json( $json );
my $definition= $data->{'myData'};
my @definition=@$definition;
print Dumper \@definition;

foreach my $record (@definition) {
	print $record->{Lang4}, "\n";
}