While you are in the Language & input menu, do not confuse it with the . The top selection changes the entire User Interface (UI). The lower selections only change the on-screen keyboard layout (e.g., QWERTY vs AZERTY).
If the touchscreen is set to a language with a non-Latin alphabet (e.g., Japanese) and you cannot navigate visually, use the physical button sequence below. This is based on the standard Eclipse menu layout.
If your AVN669HD doesn't have an English option in the settings, you can still use it effectively with these "hacks": Real-Time Translation Google Lens
