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.
When you dive into the settings (設定) of the CN-HW850D, you will not find a language toggle. Why? panasonic strada cn-hw850d japanese to english
For many, the CN-HW850D is eventually removed. The bootloader checks the region code
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. Do not attempt this unless you are a reverse engineer
You are staring at a screen full of Kanji and Kana, feeling like you need a Ph.D. in linguistics just to turn up the bass.