Try to do this in your main loop:

Qt Code: 
  1. #include <QTextCodec>
  2.  
  3. int main(int argc, char *argv[])
  4. {
  5.  
  6.   QTextCodec::setCodecForTr(QTextCodec::codecForName("UTF-8"));
  7.   QTextCodec::setCodecForCStrings(QTextCodec::codecForName("UTF-8"));
  8.   QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8"));
  9.  
  10.     QApplication a(argc, argv);
  11.     Agenda w;
  12.     w.show();
  13.  
  14.     return a.exec();
  15. }
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I did it for some especial spanish characters and it work out, maybe in your case the locale to use is not UTF-8, so you should try with another locale, but I think that it could be the solution, so you try and let us know if it work.