I've learned to read a little Japanese due to playing pokemon in Japanese, but I'm not fluent in it. ): Playing platinum and soulsilver in Japanese wasn't that difficult, since I had already played pearl and gold/crystal and even in the new areas, it was easy to figure out what to do. It looks like a lot has changed in B&W, so it they may be more difficult to play, but there will be walkthroughs that help you if you get stuck. As for those new missions, I'm sure there will be mission guides that explain what you have to do and so on.
I haven't had to rely too much on other sites when I get stuck. I got stuck in the same place as Serebii did in SS, so that site helped me get unstuck. lol Serebii will have a lot of info on the new games when they come out and that info is really helpful.
I think Marriland also does video walkthroughs of the Japanese games on youtube, so you can always watch those as well.