Not sure. The expat scene seems so vast whenever I'm back in good ol' Berlin (and more so every time). Flocks of English-speaking-people-of-all-accents everywhere I look (well inside the "groovy" parts of town of course). I wouldn't imagine anyone having to miss out on social life in Berlin, at least not due to language.
I just want to add that the fact that you are going to a country with another language is potentially a major plus point. Learning a language is one of the most enriching experiences I can think of, and hackers looking for lifehacks to keep themselves challenged should look no further.
Think about it: daily life instantly becomes gamified, a game of improving your language skills. You just have to make sure you set the scene: detach yourself a bit from the expat crowd (find local roommates for example). And then you throw yourself at it, not caring that you don’t know much in the beginning.
Especially the first year is super exhilirating: the first parties where you talk but that language, the first time you do a presentation, the first time you have a lover with whom you speak this language. Because another language is really another mental space in your head, it is a bit like you get to start over and everything feels fresh.
And then there is the aspect where speaking another language with other people is just really rich on an interpersonal level: it emports you so much of their culture. When someone talks to you about their childhood in the language of their childhood, for example, you really feel the difference.
I have to add though, that my situation is different from that of an an American, in that English is not my native language (it’s Dutch): so speaking English with Germans will always amount to us speaking through an intermediate which is neither their nor my own. So the advantages to speaking German are more immediate. As an American you have the advantage that people actually speak in your mother tongue to you.
But think about it, if you always speak English with Germans, you are always allowing them to get to know you, your culture, but you never take an effort to got to know the part of them that is in German. I’ve worked with colleagues in the Netherlands who didn’t know Dutch—and frankly, I found that after a number of years it can feel belittling: if you come to my country, but you don’t care about it’s language, it also feels like you are not really interested in me.
Of course, you can skip the German speaking folks altogether, like dualogy suggests, but missing out on a people seems to be a damn shame.
You'll be able to have a great time for sure but there will be still some locals you will have a hard time to interact with, some jokes you won't get, some shows which will make no sense to you etc. Nothing to worry about but it still can make a difference to know at least a little German.