Overall, Americans are very very cautious on the dating scene.
Your relationship together should not be based on the fact that you already speak semi-fluent Japanese. Don't Correct their English unless they ask you to. The mistakes people make in Culture Shock relationships is that they make a big deal out of the differences, and this plants the idea that you really are too different to be together.
Even thought I’ve always been attracted to Asians, even my ex had Asian features on his face, I never really considered I could be in a mix-culture relationship and make it work out leading us to marriage.
I grew older, I met people from all over the world and got a closer look for men’s behaviors.
This is an important stepping stone in a relationship (any relationship). So for example if you are in Toronto and you both love visiting art galleries make a weekly effort to go many of Toronto's art galleries. This is something you do later, after the relationship is already serious and you are perhaps even living together. Don't assume that because they are Asian that they speak other Asian languages too - like asking a Japanese person if they also speak Korean or Chinese.
This connection will cement the idea that you two really do have things in common and are not so different as society would like you to believe. Do NOT Get Language Lessons - Honestly, this is one of the worst things you can do. In fact, don't assume they even speak Japanese unless they say they do. Don't Make A Big Deal of your Language Skills - Lets pretend you already know how to speak Japanese, Korean, Mandarin, Cantonese, Vietnamese, etc.