Use…

    binmode(STDOUT, ':encoding(UTF-8)');
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…instead of…

    binmode(STDOUT, ":utf8");
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Likewise, use…

    open HASH, '<:encoding(UTF-8)', 'test_hash.txt';
    ...
    open INPUTFILE, '<:encoding(UTF-8)', 'test_input.txt';
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…instead of…

    open HASH, '<:utf8', "test_hash.txt";
    ...
    open INPUTFILE, '<:utf8', "test_input.txt";
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    my @word = $entry =~ /(\X)/g;
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    my @word = $entry =~ /(\X+)/g;
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UPDATE: Upon reexamination, it looks right to me. :-/ Using the variable name @letters instead of @word would be an improvement, though. Then…

    for my $letter (@letters) {
        my @input_features = @{ $hash{$letter} };
        print join(" ", @input_features) . "\n";
    }
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