This works by recursively constructing branches of the tree top-down and works with arbitrary "deep" keys: 
use strict;
use warnings;

use Data::Dumper;

my %properties;
while (my $propline = <DATA>) {
   next if $propline =~ /^#/;
   chomp $propline;
   my ($key, $value) = split(/=/, $propline, 2);
   _insert(\%properties, $key, $value);
}

sub _insert {
    my ($root, $key, $value) = @_;
    my ($first, $rest) = split /\./, $key, 2;
    if (defined $rest) {
        $root->{$first} = {} unless ref($root->{$first}) eq 'HASH';
        _insert($root->{$first}, $rest, $value);
    } else {
        $root->{$first} = $value;
    }
}

print Dumper(\%properties);

__DATA__

[download]
language_id.en_US=-1
language_id.es_US=-11
language_id.en_CA=-12
language_id.fr_CA=-13
langid.SPMEX=es_US
langid.FRCAN=fr_CA
altlang.US=SPMEX
altlang.CA=FRCAN
itemattr.newpart.seq=1
itemattr.newpart.name=New Part
itemattr.newpart.image1.en_US=newitem_icon.gif
itemattr.newpart.image1.es_US=newitem_icon_sp.gif
itemattr.newpart.image1.en_CA=newitem_icon.gif
itemattr.newpart.image1.fr_CA=newitem_icon_fr.gif
itemattr.watersaver.seq=2
itemattr.watersaver.name=New Part
itemattr.watersaver.image1.en_US=newitem_icon.gif
itemattr.watersaver.image1.es_US=newitem_icon_sp.gif
itemattr.watersaver.image1.en_CA=newitem_icon.gif
itemattr.watersaver.image1.fr_CA=newitem_icon_fr.gif

[download]

In reply to Re: property file parsing by pKai
in thread property file parsing by mifflin

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