No solution with Tk yet, but I conducted a little investigation, Prima on Windows suffers the same (or worse) issues with Unicode in paths returned from standard file/directory selection dialogs. But IUP appears to perform correctly in my tests:

use strict;
use warnings;
use feature 'say';

binmode STDOUT, 'utf8';

use IUP ':all';

my $dlg = IUP::FileDlg-> new( DIALOGTYPE => 'OPEN' ); # try 'DIR' for 
+folder selection

my $app = IUP::Dialog-> new( TITLE => 'Test', MARGIN => '10x10', GAP =
+> 10, child =>
    IUP::Vbox-> new([
        IUP::Button-> new( TITLE => 'Select', PADDING => '10x10', ACTI
+ON => sub {

            $dlg-> Popup;

            if ( $dlg-> STATUS != -1 ) {
                say $dlg-> VALUE;
            }
            return IUP_DEFAULT
        }),
    ]),
);

$app-> Show;
IUP-> MainLoop;
[download]

(Maybe consider this toolkit as replacement? :) Looks nice, and feature-rich and cross-platform, too.)