You have the "exportselection" backwards. Try this:

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new();
my $f = $mw->Frame(-border => 1)->pack(
   -side => "left", -fill => "both");

my $envs_list;
$envs_list = $f->Scrolled("Listbox", 
            -scrollbars=>"e",
            -exportselection => 0,
            -selectmode=>"extended")
           ->pack(-fill => 'both');

$envs_list->insert("end", "abcd");
$envs_list->insert("end", "abcd");
$envs_list->insert("end", "abcd");
$envs_list->insert("end", "abcd");

my $list;
$list = $f->Scrolled("Listbox", -scrollbars=>"e",
                -exportselection => 0,
                -selectmode=>"extended")
              ->pack(-fill => 'both');
$list->insert("end", "abcd");
$list->insert("end", "abcd");
$list->insert("end", "abcd");
$list->insert("end", "abcd");
$list->insert("end", "abcd");

$mw->Button( -text => "Selections", 
 -command => sub{
  my $selected_env_list=
      $envs_list->get(  $envs_list->curselection );                   
+                          
  my $selected_list = 
      $list->get( $list->curselection );
  
print "selected-> $selected_env_list  $selected_list\n";
       } )->pack( -side => 'left' );

$mw->Button( -text => "Exit", -command => \&exit )->pack;

MainLoop;
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