QFontDialog that uses a native dialog should be translated into system language.
However, currently only a part of the contents is translated.
See the attached image ( Qtbug85725-FontDialog.png ) when the system language is Japanese.

The right image is from font dialog of Qt app. The window title and buttons are not translated.
The left image is from font dialog of Apple's app "Notes" in the same computer.

The same phenomena can be seen in QColorDialog.