Accessing C's printf is also possible with the latest FFI::Platypus without calling an external binary:

use warnings;
use strict;
use POSIX qw/LC_NUMERIC/;
use FFI::Platypus 1.07;

my $ffi = FFI::Platypus->new( api => 1 );
$ffi->lib(undef); # search current process for symbols (libc etc.)

my $loc = $ffi->function( setlocale => ['int','string'] => 'string' )
    ->call(LC_NUMERIC, ""); # set according to environment vars
print "Locale: $loc\n";

$ffi->attach( [ printf => 'cprintf_i' ] => ['string']
    => ['int'] => 'int' ); # variadic function

cprintf_i("%'d\n", 42e6);

# ##### UPDATE - Wrapped in a sub #####

$ffi->attach( [ snprintf => 'c_snprintf_i' ]
    => ['opaque','size_t','string'] => ['int'] => 'int' );
sub commify {
    my $i = shift;
    die "Bad integer $i" unless $i=~/\A-?[0-9]+\z/;
    my $in = "$i$i";
    my $ptr = $ffi->cast('string' => 'opaque', $in);
    c_snprintf_i($ptr, length($in), "%'d", 0+$i);
    my $out = $ffi->cast('opaque' => 'string', $ptr);
    return $out;
}
print commify(42e6), "\n";
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This will print "42,000,000" for an en_US locale and "42.000.000" for a de_DE locale (this is the same behavior as /usr/bin/printf).