#!/usr/bin/perl
use strict;
use warnings;

my %country_hash;

while (<DATA>)
{
    next if /^(\s*(#.*)?)?$/; # skip blank lines and comments
    chomp; # lines that are not skipped remove new line character '\n'

    my($country,$number) = (split /:/)[0,-1]; # split line on column ':'
    
    push @{$country_hash{$country}},$number;
}

foreach my $country (sort keys %country_hash)
{
    print "$country:", join (":",@{$country_hash{$country}}), "\n";
}

=Prints
China:2:2:70
Japan:6:10
Thailand:6
=cut

__DATA__

China:wd:2

Japan:wd:6

China:sg:2

Japan:sg:10

China:kng:70

Thailand:kng:6