Anführungszeichen ersetzen: Da fehlt was.

function typografie($content)
{
 $content = str_replace (' “', ' „', $content);
 $content = str_replace ('”', '“', $content);
 $content = str_replace (' ‘', ' ‚', $content);
 $content = str_replace ('’', '‘', $content);
 $content = str_replace (' ‚n', ' ‘n', $content); // FIX: 'n/'ne
 // ... auch bei ("...")
 $content = str_replace (' (“', ' („', $content);
 $content = str_replace (' (‘', ' (‚', $content);
 $content = str_replace (' (‚n', ' (‘n', $content); // FIX: 'n/'ne
 // ... auch bei <..>"..."</..>
 $content = str_replace ('>“', '>„', $content);
 $content = str_replace ('>‘', '>‚', $content);
 $content = str_replace ('>‚n', '>‘n', $content); // FIX: 'n/'ne
 
 return $content;
}


add_filter('the_content', 'typografie');
add_filter('the_title', 'typografie');
add_filter('comment_text', 'typografie');