Both insert_after and tokens/children seem to be broken methods (or unfinished), but I've managed to get it done using __insert_after

#!/usr/bin/perl --

use strict;
use warnings;

use PPI;

my $perlcode = << "END_PERLCODE";
package My::L10N::en;

use base 'My::L10N';

our %Lexicon = (
    'Some [_1] text' =>
    'Some [_1] text',

);

END_PERLCODE

my $doc = PPI::Document->new(\$perlcode);
my $lexicon = $doc->find_first(sub { $_[1]->content eq '%Lexicon' });

my $newmsg = q{'The [_1] is in the [_2]'};
my $newtext = sprintf qq'    %s =>\n    %s,\n', $newmsg, $newmsg;
my $insert_this = PPI::Document->new(\$newtext);


#~ use PPI::Dumper;
#~ print __LINE__,"\n"; PPI::Dumper->new( $lexicon->parent )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $lexicon->parent->last_token
+ )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $lexicon->parent->last_token
+->previous_token )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $lexicon->parent->last_token
+->previous_token->previous_token )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $insert_this->find_first('St
+atement') )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $insert_this->find_first('St
+atement')->tokens )->print;
#~ print __LINE__,"\n"; PPI::Dumper->new( $insert_this->find_first('St
+atement')->children )->print;


$lexicon->parent->last_token->previous_token->previous_token
->__insert_after( $insert_this);

print $doc->serialize();


__END__
package My::L10N::en;

use base 'My::L10N';

our %Lexicon = (
    'Some [_1] text' =>
    'Some [_1] text',

    'The [_1] is in the [_2]' =>
    'The [_1] is in the [_2]',
);
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