I did not find German girls to be anywhere near as approachable as pretty much any other nationality of European during the time I lived in the country. The vast majority of my bangs were foreign girls who were living or traveling in Germany (Brazilians, Poles, the occasional South or North American).
I casually dated a few German girls and went on more first dates than I can count. Most of them were sweet, normal girls in the 6-7 range who were just a little too career-driven for my tastes, and in general were all socialized to be culturally autistic and unfriendly to strangers because that's just how Germany is. So nothing ever developed except for sexual flings of a few weeks or months. I can't tell you how a German girl would be as a wife or LTR. But approach and first date-wise, they can be as cold and robotic as the stereotypes suggest, or totally open and friendly - it all depends on context, as German thinking tends to be to regiment everything to its proper time and place, including meeting new people (thus the existence of bacchanal beer fests, like Oktoberfest).
I never got eye contact from German girls on the street. Ever. I don't think I did a single day approach because I almost never saw an IOI. On the other hand I get IOIs all the time in other countries, like Poland, where I am now. It's context. For example, my friend picked up a smoking hot girl on the airplane when she was with her mom. She was traveling and was in a mood to socialize. Girls in bars are (obviously) a lot more open to meeting people, although they are going to say some dumb shit to you 9/10 times if you are American about how Trump sucks or nobody can possibly have a good life in the USA because of... reasons. I have no idea, I always just tuned that shit out when it started.
But regardless of all that, typically in bars if a girl gave me eye contact and I approached her, within a few minutes they were warm and flirtatious and the typically cold exterior melted (it should go without saying that I mean if the girl was into me - if she was not, however, I don't think German girls gave worse/ruder blowouts than anywhere else, although they are usually much more direct and to the point about the fact they're not interested).
In casual dating/hooking up, most of them did the typical Northern European thing of playing the game of who cares the least while still being willing to fuck from the 1st or 2nd date on. Only one German girl I dated, would I say acted in a feminine way that showed me really cared about me from early on. I am a man who likes feeling appreciated by my woman, even if she's only a plate and we don't see other often, and this does not seem to me common in German dating culture - at least for a while, until things get serious. A close friend of mine (Bavarian native) said when he was growing up it was common for his group of friends to fuck each other's exes and make fun of the guy who got would actually get pissed/emotional about it. Different world I guess.
One plus side I don't see mentioned often re: German women is the looks. Germany has a high concentration of stunners - and I mean some of the most beautiful faces and bodies I have seen in 30+ countries of travel and four years of living abroad - at least in Hamburg and Munich, which are more "posh" rather than hipster cities. I don't know why these two cities are not more hyped for their beauty level, as it is off the charts. If you have a big bankroll and speak German I imagine it could be exceptional. I don't have either so for me the German 8's and up were a no-fly zone...