As usual, the final solution was a bit more complicated than I thought, but I wanted to provide a final update in case others have the same issue.

The attached code shows what I did in order to translate unicode characters into ASCII with Text::Unidecode. This will translate the entire string on each keystroke, and works with cut-n-paste as well.

NOTE: when using a text variable for the text in the entry, you cannot simply re-assign text to it in the validatecommand() sub. One trick is to use afterIdle() to do that later.

Thanks again to all for the help!

Craig

#!/opt/homebrew/bin/perl

use strict;
use warnings;

use Data::Dumper;

use Tk;
use utf8;
use Text::Unidecode;

my $mw = MainWindow->new();
my $textvar;

my $e = $mw->Entry(-textvariable => \$textvar,
    -validate => 'key',
    -validatecommand => sub {
        my ($new,$changed,$old,$ix,$type) = @_;
        return 1 if (!defined($changed));
        return 1 if ($new eq "") or ($type<0);
        $mw->afterIdle(sub{
            $textvar = unidecode($new);
            print STDERR "ASCII: $textvar\n";
        });
        return 1;
    },
)->pack();

MainLoop;
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