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

use XML::LibXML;

my $dom = 'XML::LibXML'->load_xml(location => 'file.xml');
for my $child (
    @{ $dom->find('/trans-unit/*[self::source | self::target]') }
) {
    ( my $contents = join '', $child->childNodes ) =~ s,\n, <lb/> ,g;
    print $contents, $child->nodeName eq 'source' ? ' || ' : "\n";
}