...but with that inspiration I did some kind of brute force workaround which seems to work for me, though it appears to be quite ugly.
I am very open for better ideas, especially concerning the performance...
Qt Code: 
  1. QString MainWindow::fixUtf8BrokenString(QString text)
  2. {
  3.     int index = text.indexOf(QChar(195));
  4.     while (index>=0)
  5.     {
  6.         if (text.count()>++index)
  7.         {
  8.             int code;
  9.             code=text[index].toAscii();
  10.             switch (code)
  11.             {
  12.             case  128: text.replace(QString(QChar(195))+QString(QChar(128)),"À");break;
  13.             case  129: text.replace(QString(QChar(195))+QString(QChar(129)),"Á");break;
  14.             case  130: text.replace(QString(QChar(195))+QString(QChar(130)),"Â");break;
  15.             case  131: text.replace(QString(QChar(195))+QString(QChar(131)),"Ã");break;
  16.             case  132: text.replace(QString(QChar(195))+QString(QChar(132)),"Ä");break;
  17.             case  133: text.replace(QString(QChar(195))+QString(QChar(133)),"Ã…");break;
  18.             case  135: text.replace(QString(QChar(195))+QString(QChar(135)),"Ç");break;
  19.             case  136: text.replace(QString(QChar(195))+QString(QChar(136)),"È");break;
  20.             case  137: text.replace(QString(QChar(195))+QString(QChar(137)),"É");break;
  21.             case  138: text.replace(QString(QChar(195))+QString(QChar(138)),"Ê");break;
  22.             case  139: text.replace(QString(QChar(195))+QString(QChar(139)),"Ë");break;
  23.             case  140: text.replace(QString(QChar(195))+QString(QChar(140)),"Ì");break;
  24.             case  141: text.replace(QString(QChar(195))+QString(QChar(141)),"Í");break;
  25.             case  142: text.replace(QString(QChar(195))+QString(QChar(142)),"ÃŽ");break;
  26.             case  143: text.replace(QString(QChar(195))+QString(QChar(143)),"Ï");break;
  27.             case  144: text.replace(QString(QChar(195))+QString(QChar(144)),"Ð");break;
  28.             case  145: text.replace(QString(QChar(195))+QString(QChar(145)),"Ñ");break;
  29.             case  146: text.replace(QString(QChar(195))+QString(QChar(146)),"Ã’");break;
  30.             case  147: text.replace(QString(QChar(195))+QString(QChar(147)),"Ó");break;
  31.             case  148: text.replace(QString(QChar(195))+QString(QChar(148)),"Ô");break;
  32.             case  149: text.replace(QString(QChar(195))+QString(QChar(149)),"Õ");break;
  33.             case  150: text.replace(QString(QChar(195))+QString(QChar(150)),"Ö");break;
  34.             case  152: text.replace(QString(QChar(195))+QString(QChar(152)),"Ø");break;
  35.             case  153: text.replace(QString(QChar(195))+QString(QChar(153)),"Ù");break;
  36.             case  154: text.replace(QString(QChar(195))+QString(QChar(154)),"Ú");break;
  37.             case  155: text.replace(QString(QChar(195))+QString(QChar(155)),"Û");break;
  38.             case  156: text.replace(QString(QChar(195))+QString(QChar(156)),"Ü");break;
  39.             case  157: text.replace(QString(QChar(195))+QString(QChar(157)),"Ý");break;
  40.             case  158: text.replace(QString(QChar(195))+QString(QChar(158)),"Þ");break;
  41.             case  159: text.replace(QString(QChar(195))+QString(QChar(159)),"ß");break;
  42.             case  160: text.replace(QString(QChar(195))+QString(QChar(160)),"Ã ");break;
  43.             case  161: text.replace(QString(QChar(195))+QString(QChar(161)),"á");break;
  44.             case  162: text.replace(QString(QChar(195))+QString(QChar(162)),"â");break;
  45.             case  163: text.replace(QString(QChar(195))+QString(QChar(163)),"ã");break;
  46.             case  164: text.replace(QString(QChar(195))+QString(QChar(164)),"ä");break;
  47.             case  165: text.replace(QString(QChar(195))+QString(QChar(165)),"Ã¥");break;
  48.             case  166: text.replace(QString(QChar(195))+QString(QChar(166)),"æ");break;
  49.             case  167: text.replace(QString(QChar(195))+QString(QChar(167)),"ç");break;
  50.             case  168: text.replace(QString(QChar(195))+QString(QChar(168)),"è");break;
  51.             case  169: text.replace(QString(QChar(195))+QString(QChar(169)),"é");break;
  52.             case  170: text.replace(QString(QChar(195))+QString(QChar(170)),"ê");break;
  53.             case  171: text.replace(QString(QChar(195))+QString(QChar(171)),"ë");break;
  54.             case  172: text.replace(QString(QChar(195))+QString(QChar(172)),"ì");break;
  55.             case  173: text.replace(QString(QChar(195))+QString(QChar(173)),"Ã*");break;
  56.             case  174: text.replace(QString(QChar(195))+QString(QChar(174)),"î");break;
  57.             case  175: text.replace(QString(QChar(195))+QString(QChar(175)),"ï");break;
  58.             case  177: text.replace(QString(QChar(195))+QString(QChar(177)),"ñ");break;
  59.             case  178: text.replace(QString(QChar(195))+QString(QChar(178)),"ò");break;
  60.             case  179: text.replace(QString(QChar(195))+QString(QChar(179)),"ó");break;
  61.             case  180: text.replace(QString(QChar(195))+QString(QChar(180)),"ô");break;
  62.             case  181: text.replace(QString(QChar(195))+QString(QChar(181)),"õ");break;
  63.             case  182: text.replace(QString(QChar(195))+QString(QChar(182)),"ö");break;
  64.             case  184: text.replace(QString(QChar(195))+QString(QChar(184)),"ø");break;
  65.             case  185: text.replace(QString(QChar(195))+QString(QChar(185)),"ù");break;
  66.             case  186: text.replace(QString(QChar(195))+QString(QChar(186)),"ú");break;
  67.             case  187: text.replace(QString(QChar(195))+QString(QChar(187)),"û");break;
  68.             case  188: text.replace(QString(QChar(195))+QString(QChar(188)),"ü");break;
  69.             case  189: text.replace(QString(QChar(195))+QString(QChar(189)),"ý");break;
  70.             case  191: text.replace(QString(QChar(195))+QString(QChar(191)),"ÿ");break;
  71.             }
  72.         }
  73.         index = text.indexOf(QChar(195));
  74.     }
  75.     return text;
  76. }
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