use 5.024;
use autodie;
use Encode qw( decode encode );
use HTML::Entities;
use URI::Escape;

open (my $fh,'<','t.txt');
my $content;
{
    local $/ = undef;
    $content = <$fh>;
}

$content = decode('UTF-8',$content,Encode::FB_CROAK);
$content = decode_entities($content);

my @terms = (
    "\N{LATIN SMALL LETTER A WITH DIAERESIS}",
    "\x{e4}",
    chr 228,
    decode('UTF-8',"\xc3\xa4"),
    decode('UTF-8',uri_unescape("%c3%a4")),
);

for my $term (@terms) {
    my $for_terminal = encode('UTF-8',$term);
    while ($content =~ /$term/g) {
	say "Treffer: '$for_terminal' an Position " . pos $content;
    }
}