Save the Panasonic unit in a box in your garage. If you ever sell the car to a Japanese buyer, you can reinstall it in 30 minutes. But for your daily commute, embrace the aftermarket. Your blood pressure will thank you. Panasonic Strada CN-HW850D Japanese to English, convert JDM navigation, Panasonic Strada English firmware, CN-HW850D language hack, JDM head unit translation.
The bootloader checks the region code. Forcing an export ROM bricks the unit (black screen of death). Recovery requires a JTAG programmer and soldering skills. Do not attempt this unless you are a reverse engineer. Option B: The "Hybrid" Board Replacement (Not worth it) Some Japanese shops offer a service to replace the main logic board with one from a non-JDM wreck. Cost: ~$500-$700 USD + shipping. You lose the Japanese TV tuner (no loss) but often lose the reverse camera compatibility.
Pro tip: Print this table as a sticker and place it on your sun visor. Is it possible to truly convert the Panasonic Strada CN-HW850D from Japanese to English?
No, not without destructive, expensive, and highly technical work that risks bricking the unit.