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Hi there - I'm the author of this piece. I don't actually speak German. I'm trying to improve - however, I wouldn't say it's required in Germany to start something on your own. Many of the meetups are in English and everyone I've spoken to is fluent. I think it's another story if you're trying to get a job though...
Yes, the hardest thing is probably to get a flat and register a business without speaking German and these are one time things, no ongoing stuff. The start-up scene speaks English fluently and buying stuff etc. doesn't need much talking. The start-up I work with has 2 employees who don't speak German at all and they say it's only a problem when they are in smaller villages.
If you want to incorporate a business, you do not necessarily have to do it in Germany, it is the EU after all.