My first girlfriend and I were 'facebook' official and we used that as a way of telling our friends. Took a lot of the work out of telling mutual friends.
Lately, if I ever get serious with someone, no way that's going on facebook. I dated a girl for a while who was super into facebook and the minute I asked her to be exclusive, she went to update her facebook status. It felt pretty tacky and kind of felt like attention seeking behaviour from her. I didn't update my status. She never said anything but I got the impression she was a little hurt by this. We broke up after a short period of time and she was engaged to someone within the next year, documenting every step of the process from engagement to the wedding on facebook. Too much man.
On dating Japanese women, I can't give too much advice. I've gone on a handful of dates with one Japanese woman and her approach to dating was very reserved. She preferred to pursue friendship with someone and if either person developed feelings for the other they would 'confess their love' (her words) for one another and become boyfriend girlfriend on the spot. No kissing or any kind of physical intimacy up until that point. Obviously I noped out of that pretty quick.
I'm sure not all Japanese women are like this, particularly ones who have been living in the West for a couple of years. People are different though. There are no specific tips. With regard to language barriers, just be aware that she may have difficulties interpreting things like sarcasm and other nuances in communication that derive from the tone of your voice and certain slang or expressions may be interpreted literally if she's never heard them before. I'd say the importance of clear communication is more important with people for whom English is a second language.