use strict;
use warnings;
use v5.14;
use autodie;

my %word_sets;

while( <> ) {
    chomp;
    my ( $conjugation, $infinitive ) = split /\s*\|\s*/;
    push @{ $word_sets{ $infinitive }, $conjugation;
}

open my $outfh, '>', 'combined_conjugations.txt';
while( my( $infinitive, $conjugations ) = each %word_sets ) {
    next unless @{$conjugations} > 1; # Skip items that didn't appear twice.
    say $outfh join( ' | ', $infinitive, @{ $conjugations } );
}
close $outfh;