There is currently no way to choose the left/right orientation of the default window buttons, this depends on the system. However, respecting OS user settings (like in Ubuntu) would be a potential improvement. We already account for locale-dependent orientation.
You can find out the actual location of the window buttons by inspecting the HeaderBar.leftSystemInset(Stage) and HeaderBar.rightSystemInset(Stage) attached properties. Both properties will tell you if there is a system-reserved area on the respective side of the window; if there isn't, the reported area will be empty.
