Seems the japanesse FW has written additional information in the nuvi file system and in the GarminDevice.xml file there is some kind of japanesse characters. I read about similar problem in the polish garniak forum regarding modified SG/MAL FW for nuvi 12xx series.
Code:
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Don't think this is something to worry about.

Ok, here what you can try to fix that. Perform them step by step.
1. Master Reset
2. Clearing of the nuvi Non-Volatile memory
3. Downgrade to version 3.90 then again update to 5.40.

FW 3.90:
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