package Foo;

use base qw/Bar::Unicode Bar/;

__PACKAGE__->prepare_parameters;


package Bar;

sub prepare_parameters {
    my $class = shift;

    # initialize parameters...
}


package Bar::Unicode;

use NEXT;

sub prepare_parameters {
    my $class = shift;

    # let parent initialize parameters
    $class->NEXT::prepare_parameters;

    # utf8 encode parameters...
}