display csv in browser with charset utf-8, using php and headers

Question

In a cloud-like web application I want to display files directly in browser, which works perfectly for .PDF and images using this code:

if (file_exists($serverfile)) {
    header('Content-Type: ' . mime_content_type ($serverfile) . '; charset=utf-8');
    header('Content-Disposition: inline; filename="' . $origname . '"');
    header('content-Transfer-Encoding: binary');
    header('Content-length: ' . filesize($serverfile));
    header('Accept-Ranges: bytes');
    readfile($serverfile);
    //... more unrelated code
    exit;
}

but I have scrumbled characters e.g. with German Umlauts, in case the file is a .CSV

I also set ini_set('default_charset', 'utf-8'); on top of the script.

What am I missing ?