$rs = $db->resultset('Comment')->search({
    'country.language_id' => \'= country_2.language_id', # literal SQL
}, {
    prefetch => [
        { user => { country => 'language' } },
        { artwork => { artist => 'country' } },
    ],
});

while ( my $comment = $rs->next ) {
    say sprintf('%s : %s said about "%s" (%s) : "%s"',
        $comment->user->country->language->name,
        $comment->user->name,
        $comment->artwork->name,
        $comment->artwork->artist->name,
        $comment->text,
    );
}