First, the questions:
Is it easy to meet other fellow single people in Germany?
I think that depends on where you are. I think in the big city (I'm in Berlin) it's easy, but not necessarily easy to find a relationship if that's what you're looking for (I was, when I was dating). Berlin is full of people who are only here short-term, and a lot of people are only looking for flings (even the people who live here permanently). I found that was the case when I was dating a decade ago, but I imagine that Tinder has brought out a lot more of that.
I don't think it's different than any other big city in any other country in that respect, though.
How do you go about meeting people (through friends, online dating, apps, meetup groups)?
Well, I met my husband on a dating site, so I can attest that it can work out haha. Meetups, hobbies (join a workshop, sing in a choir, play a sport), and through friends can be good bets. Plus, you might make local friends in the process. Even if you don't find a relationship, having locals as friends is always good.
Like TominStuttgart mentioned above, don't just approach someone on the street or in a shop and ask them out. That's weird.
How safe is it to date in Germany?
As safe as it is anywhere else in Europe. If you meet someone online, always use caution and trust your gut. The vast majority of people are just looking for dates and won't hurt you, but you never know if you get the one that will.
How do you deal with cultural differences when dating?
Talk about it. Always talk about it.
What are certain dating etiquettes and rules when dating in Germany?
Don't expect the man to pay, and if you're a man, be ok with splitting the bill! I've talked about this with my (local) girlfriends a lot, and we all agree that we're not really into this. A lot of us feel that it implies that we aren't equals on the date, and some of us get nervous that you might expect something. Probably a few women like it, but most don't...at least that's the case in Berlin.
How do you deal with getting into a serious relationship if you know you might be leaving Germany?
I'm a German citizen and always intended to stay, so I can't speak about this personally. I'd recommend always talking about this as early as possible. If you absolutely don't want to stay and they don't want to move with you back to your country, you should end things before it gets serious. If you're open to staying and/or they're open to leaving, then you can see where things go and where the relationship takes you.
Anyway, a few other notes....I'm married and I haven't dated in a few years. I think it's changed a lot, especially in Berlin. A lot of my single friends use Tinder, and the whole dating scene sort of scares me and I'm glad I don't have to do it anymore. I think there are also huge generational differences. When I was young and single, I used to have a friend who was 15 years older than me and she was very "traditional" in that she thought that you should never call a guy, ask a guy out, etc. But I think that's fine for my generation (I'm an older millennial). Younger millennials also have their own rules. Also, I was barely an adult when I moved here and had almost no dating experience where I grew up (Canada), so I don't have much to compare it to. I did all of my dating in Berlin....