I'm pretty sure at work they understand German, too.
Also, you can think in German at any time of the day.
Even more: Of these 80% there are surely many that also would love to get better in German: Why not also agree to converse with them in German, too?
While there is some small element of truth in it, this only holds if you are new in Germany (and mostly because of politeness). If you live there for a longer time and don't work on your German, it will turn the other way round.
My advice - if you really want to move abroad, move to the US, much less issues overall and English is way simpler up to C2 level (which gets super hard) and you can get a recognition and make a bank way easier.
That's not true. The typical German mentality is rather: They are/were willing to learn English to be able to communicate with you when you came. But now that you want to stay here for a longer time, you are expected you to learn German, too. So in other words: Some English speakers rather tend to confuse politeness (speaking English at the beginning to native English speakers when they are new to Germany) with acceptance (of having to speak in English to people that stay there for a longer time and are not willing to learn German).
It's good training in not worrying too much about what other people think of you. What's the harm really in someone thinking you're an idiot? You know it's not the case.
Swallowing your pride speeds up learning immensely. You can even have fun with it--people will see you as funny and non-threatening, which can actually translate to likability quite easily if you don't get a chip on your shoulder about it.
My heart was elsewhere the whole time, so I'm not the best person to ask :P Germany itself was enjoyable, and I've met some fairly friendly Germans in WGs. It rains a lot in some places. YMMV, good luck!
My wife needed a few weeks to be able to speak Norwegian on a conversational level, I didn't need much more than that for German (difficult to count exactly due to travelblah). Once you reach conversational level the rest of the way has a different quality — you'll need to learn more but you've conquered the cliff, the rest is a modest incline.
Recently I even got complimented by a McD employee for telling them my rather lengthy order flawlessly without any need for interruption, made my day ;-D
And btw I didn't downvote the parent. My point was mostly tangential rather than a counter argument.
You guys must be both geniuses. Either that or those "learn X language in 14 days!" books actually work.