@Pardeep said in Japanese letters in file path converted into question mark(?). How can i deal with them?:

qDebug()

This is simply debug output, it can depend on the encoding in the console. Try

qDebug()<<fileName1.toUtf8()<<"\nExist: "<<f1.exists();

hi
I started with
http://doc.qt.io/qt-5/internationalization.html

and then
the "Dynamic Language Switching"
from this book
http://www.bogotobogo.com/cplusplus/files/c-gui-programming-with-qt-4-2ndedition.pdf

On windows you can change the locale to test if it will switch. I assume
you can do the same in OSX.