I'm not sure if I understand the question, but this may help. I asked something similar to this awhile back, where there were encoding problems in finding files in a directory. graff showed me this:

#this decode utf8 routine is used so filenames with extended
# ascii characters (unicode) in filenames, will work properly
use Encode;
opendir my $dh, $path or warn "Error: $!";
my @files = grep !/^\.\.?$/, readdir $dh;
closedir $dh;
# @files = map{ "$path/".$_ } sort @files;
#$_ = decode( 'utf8', $_ ) for ( @files );
@files = map { decode( 'utf8', "$path/".$_  ) } sort @files;
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I don't know if Tk's getOpenFile is buggy or not, but graff said that once you pass the filename through decode, Perl will tag it as unicode and do the right thing. Maybe you could make your own "custom-file-dialog" that preprocesses the dirlist with decode?