I stayed and worked as a Lawyer in Japan for a few years, and I wouldn't say it makes a difference whether you want to integrate or not. I would even tend to think that not integrating can result in being better accepted. Just be the French or the US guy they like to hang out with, the one who knows to do stuff they don't know, and everything will be fine. Try to become a japanese, and you'll end up being crushed by the system.
Speaking japanese is a great plus of course - but it's quite easy to learn, reading and writing don't help much - except if you want to explore the vast trove of japanese culture.
But the most important thing is to know that there is nearly zero interest in working in Japan if you're not the boss. Your career will be painful and difficult. You will suffer. It's a worst of two worlds situation.
Speaking japanese is a great plus of course - but it's quite easy to learn, reading and writing don't help much - except if you want to explore the vast trove of japanese culture.
But the most important thing is to know that there is nearly zero interest in working in Japan if you're not the boss. Your career will be painful and difficult. You will suffer. It's a worst of two worlds situation.