Have you considered installing your own private Perl library then? Installing locally is easy for modules that you can simply copy, like CGI.pm. I haven't look at a workaround to make PREFIX work with Debian, so you'll have some trouble if you want to install Perl modules locally using the standard <c>perl Makefile.PL PREFIX=~moritz/perl-lib; make test; make install

Sooner or later I'll have to do that I think.

My current approach is a wrapper (not yet tested), I haven't decided yet which approach I like better (or which I detest less ;-)

package MyCGI;
use base CGI;
use strict;
use warnings;
use Encode qw(encode);

sub param {
    my $self = shift;
    if (@_ == 1){
        my @val = $self->SUPER::param(@_);
        @val = map { encode("utf8", $_) } @val;
        return wantarray ? @val : $val[0];
    } else {
        return $self->SUPER::param(@_);
    }
}
1;
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Watch out for file upload fields: if you utf-encode $q->param('upload'), you'll mangle the underlying filehandle. I use an override that's pretty much the same as yours, except that I added the following check:

sub param {
    my $self = shift;
    if (@_ == 1){
        my @val = $self->SUPER::param(@_);
        @val = map { maybe_decode( $_ ) } @val;
    # rest of your param()
}

sub maybe_decode {
    my $p = shift;
    return ( !$p || ( ref $p && fileno($p) ) )
           ? $p
           : encode('utf8', $p);
}
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