php functions based on mbstring/preg_match that will detect utf8 and fix German encoding if no utf8 is detected.

scheiss-encoding.php

<?php
//SCHEISS ENCODING!!!
//via: http://php.net/manual/de/function.mb-detect-encoding.php#68607
function detectUTF8($string){
        return preg_match('%(?:
        [\xC2-\xDF][\x80-\xBF]        # non-overlong 2-byte
        |\xE0[\xA0-\xBF][\x80-\xBF]               # excluding overlongs
        |[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}      # straight 3-byte
        |\xED[\x80-\x9F][\x80-\xBF]               # excluding surrogates
        |\xF0[\x90-\xBF][\x80-\xBF]{2}    # planes 1-3
        |[\xF1-\xF3][\x80-\xBF]{3}                  # planes 4-15
        |\xF4[\x80-\x8F][\x80-\xBF]{2}    # plane 16
        )+%xs', $string);
}

function fixEncDe($string) {
    if(!detectUTF8($string)) {
        //if no utf8 chars detected, let's assume it's the usual ISO-BS and convert, dropping all invalid chars on the way:
        ini_set('mbstring.substitute_character', "none"); 
        $string= mb_convert_encoding($string, 'UTF-8', 'ISO-8859-15');
        return $string;
    } else {
        //nothing to do, if $string is already utf8
        return $string;
    }
}
?>