Perhaps something like this?

use strict;
use warnings;
use 5.012;
use Data::Dumper;

my @file1 = (
'this is an example.',
'the example is just for display.',
'how to solve it in an efficient way?',
);

my @file2 = (
'este es un ejemplo.',
'el ejemplo es sólo para mostrar.',
'cómo resolverlo de una manera eficiente?',
);

say Dumper(parse(@file1));
say Dumper(parse(@file2));

sub parse {
    my @sentences = @_;
    my %words_catalogue;
    my $line = 1;
    for my $sentence (@sentences) {
        my @words = split ' ', $sentence;
        $words_catalogue{$_}{$line}++ for @words;
        $line++;
    }
    return \%words_catalogue;
}
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The split into words is very naive and you will have to look into it. Perhaps first discarding punctuation and the like. Still the idea should be clear.