How to can I change the screen language in Japanese cars?

I would like to make money buy going to a car dealership that sell Japanese manufactured cars and changing the built-in Tomtoms language. It would be easy but it's all in Japanese! I don't want to be too specific with the car manufacturer but I'll just day for example, Honda. I know that different models have different Tomtoms so I'll just day the Honda Fit and the builders of the Tomtom is something like 'Eclipse'. Can someone please help?

The issue with many of them is you can't change the screen language you need to reprogram the car.
This is why Grey imports have issues.
If it was simple everyone would do it.
The sat nav will also be carrying maps of Japan not of the country it was imported to.

Most JDM cars come with Japanese only navigation / entertainment systems. They were never intended to be used outside Japan, so they never installed any other language.

The only practical option is to replace them with an after market system. You can buy them that integrate with the reverse camera etc, but if they include the climate controls, you are probably out of luck.