Panasonic patched the 5189 exploit in firmware version 4.2. You cannot downgrade. However, you can use the "Partial Overlay" method:
The Panasonic CN-MW240D is a car navigation system in the Strada series. It features a 2-DIN, 7-inch widescreen monitor and supports terrestrial digital broadcasting. Unlike smartphone-based navigation, this dedicated device uses an SD memory card to store map data and other essential files. panasonic cnmw240d change language exclusive
Many Panasonic navigation units have a hidden service menu that allows you to toggle the language. This is the first thing you should try. Panasonic patched the 5189 exploit in firmware version 4
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