Panasonic patched the 5189 exploit in firmware version 4.2. You cannot downgrade. However, you can use the "Partial Overlay" method:
: Some third-party specialists offer "English conversion" services, which involve rewriting the unit's firmware. This is not an official Panasonic service and typically requires sending the unit to a technician or purchasing a specific SD card update. Remote Control Access panasonic cnmw240d change language exclusive
Look for 言語 (Gengo) or a globe icon. Panasonic patched the 5189 exploit in firmware version 4