use utf8 affects string literals in the source (and STDIN and STDOUT?). Strings stored in a data file won't be affected by it.

Simply specify the encoding of the data file when opening the data file. 

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

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If the you have a handle and not a file name, use binmode. 

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

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Or decode the string explicitly 

use Encode qw( decode );

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

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Output is very similar. Set the encoding on the output handle or use encode. 

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

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

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

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Update: Added output info.

In reply to Re: Coding for multiple Languages by ikegami
in thread Coding for multiple Languages by cosmicperl

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