Writing System in QFontDialog?

[ashukla]

void setWritingSystem ( QFontDatabase::WritingSystem script )
This property holds the writing system that serves as a filter for the combobox.
If script is QFontDatabase::Any (the default), all fonts are listed.

It only filter the Font Families; but does not change the required language. However still it is a problem of setting the writingSystem of QFontDialogBox.

Please view the experts the problem & suggest;
But how a way I am swiching languages according to writingSystem & font families.