Second interview - what’s next?

Hello everyone, I'm hoping that someone could shed some light on a situation I'm currently in. I am a Malaysian-born Chinese and am in the process of being interviewed by a company in Japan (through Skype video & a series of tests). The interview took place since 3 weeks ago and is now entering the 4th week. To cut the long story short, basically I have went through a first interview with HR, then did some work and personality tests, and have also gone through the second interview last week (mid-week) with several managers for almost 1.5 hours. Overall it went pretty well and I've been told that my experience/skills are pretty impressive. Now as we are entering the mid-week of the 4th week, I have not heard from them at all (though last week the HR did mention that she would contact me again). In this case, I have a few doubts:

1) How long does it usually take for a JapANESE company (actually it's more of a foreigner's company as the founder is a foreigner with 50% JapANESE employees) to decide to hire a foreigner from overseas?
2) At this point, should I write a follow-up email to them?

Thanks a lot! Any response will be much appreciated.

I can't answer #1, but perhaps #2 wouldn't hurt if you've been waiting that long.

You HR interview was to simply cut out the fluff from getting to the real interview. Which you wrote was last week with several managers. So really it has only been a week (or a little less) since you had your interview. That's not very long at all considering you probably weren't the only candidate they were interviewing.

1) How long does it usually take for a JapANESE company (actually it's more of a foreigner's company as the founder is a foreigner with 50% JapANESE employees) to decide to hire a foreigner from overseas?

Depends on the company. It can happen pretty fast (like within a few weeks) but considering your last interview was just last week I'd stay you're still quite early in the process to have heard back yet. Depending on how many candidates they have, they may not have even finished this round of interviews yet.

2) At this point, should I write a follow-up email to them?

Did you send a thank you email after the interview? If not, then now would be a good time to fire one off.

I would not send a thank you email an entire week later. That doesn't look good. I think I'd wait until 2 weeks have passed before I'd send them a message about the results of the interview.

Thanks guys, for your responses & clarifications. Just wanted to give you a small update here - they have contacted me to go for a third round of interview. While having 3 rounds of interview is not extremely rare, I couldn't help but to wonder if having so many stages of interview is common in Japan. I think I won't be surprised if there will be a 4th interview after this because I really feel like it will never end... lol

Yes, it's pretty normal to have several interviews in Japan, don't worry!
Ganbatte!

I would not send a thank you email an entire week later. That doesn't look good.

It is better to send a thank you immediately, but considering I've read that something like 25% of hiring managers say they ONLY consider those who write thank you notes...