I resolve it.
I setted font of text as property of QML Text component.
(Like font.family : parent.fontfamily)
and on Qt 5.7's QML, there are no enough options to control font properties.
so, I moved to C++ side and set a whole application font.
QFont font = someClass.getLangFont();
//set property of font instance here
// such as hinting policy, style etc.
now it looks very cleary...