After reformatting your posted code, I get something like:

#!/usr/bin/perl -w
use strict;

my @findle = ("fever","febbre","la fièvre","koorts");
my $size = @findle;
my $number = 0;
for (my $i=0; $i<$size; $i++) {
    if ($_ =~ /$findle[$i]/ ) {
        print "$_\n";
        $number++;
        #@lines = # print ("there are : " . $number);
    }
}
[download]

which can be written more cleanly as Your code can be written more cleanly as

#!/usr/bin/perl -w
use strict;

my @findle = ("fever","febbre","la fièvre","koorts");
my $number = 0;
for my $element (@findle) {
    if (/\Q$element\E/) {
        print "$_\n";
        $number++;
        #@lines = # print ("there are : " . $number);
    }
}
[download]

If you want to cache the elements you hit on, you can combine an array outside the scope of your test with push:

#!/usr/bin/perl -w
use strict;

my @findle = ("fever","febbre","la fièvre","koorts");
my @hits;
for my $element (@findle) {
    if (/\Q$element\E/) {
        print "$_\n";
        push @hits, $element;
        #@lines = # print ("there are : " . $number);
    }
}
[download]

Note that the length of your @hits array also functions to count the number of hits.

Update: OP added tags, so modified above accordingly.