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open(my $fh, '<:encoding(UTF-8)', $language_qfn) or die;
while (<$fh>) {
   ...
}

binmode(STDIN, ':encoding(UTF-8)');
while (<STDIN>) {
   ...
}

use Encode qw( decode );

...
   $_ = decode('UTF-8', $_);
   ...
}

open(my $fh, '>:encoding(UTF-8)', $output_fqn) or die;
print $fh ($text);

binmode(STDOUT, ':encoding(UTF-8)');
print($text);

use Encode qw( encode );
open(my $fh, '>', $output_fqn) or die;
print $fh (encode('UTF-8', $text));