Hmm I think it would be better to apply this only to Windows build (you said in Linux it works well). You may wrap this code with:
Qt Code: 
  1. #ifdef Q_OS_WIN32
  2.   label.setFont(QFont("Dejavu Sans"));
  3. #endif
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Look at http://doc.qt.io/qt-4.8/QtGlobal for platform preprocessor definitions and don't forget to include Dejavu (or any other font you want use for Braille) into your distribution package for Windows.