If you cannot locate the language setting because a previous owner set a passcode or the touch calibration is off, you must perform a hardware reset.
If you are trying to navigate the menus manually, look for these characters: 設定 (Settei) : Settings / Setup メニュー (Menyū) 音量 (Onryō) 現在地 (Genzaichi) : Current Location (Navi) 画面 (Gamen) : Screen settings 言語 (Gengo) Eclipse Avn669hd Change Language
This is the standard method if the system is functioning normally. If you cannot locate the language setting because
: You can find discussions and professional advice on forums like JustAnswer where technicians specifically address the AVN669HD model. Eclipse Avn669hd Change Language