I re-wrote your question and I put you in the right Category :>)
Your unit, only available FROM Japan, and as Larry says many are for the Japanese home market only, and a sold ONLY in Japanese language.
There is help here
Car Electronics Technician: Russell H.
The question about the problem, with a GPS or stereo device in a car, that turns out to have an interface in Japanese is, whether the car it is in was intended for the Japanese market.
Generally, in a car that was intended to be sold in Japan, the language in the included devices is in Japanese and has no capability to switch language, unfortunately. Is it possible that your car is indeed an intended-for-Japanese-market car?
I am looking up the info on changing the language for that model, if it is possible. I will post later with that information, if I can find it.
On the main screen, touch the triangle with the gear icon.
Then the first entry should be the System Language (no matter what it looks like in Japanese kanji, it should be at the top of the gear-icon Settings screen.)
Touch the language displayed there (whatever it looks like) and see whether there is any choice that looks like
If none of the language choices are in anything but Japanese kanji characters, then you may have to work through each choice, seeing whether it changes the interface to something else than Japanese kanji characters, until you hit upon one that matches what you need... regrettably there may be no other practical way of getting to the objective here.
You can also use a Smartphone and with the Google Translation app, use the Camera feature to translate what you are seeing. Look for Settings - Language