In Prague we have a comparable housing problem to Berlin but all the politicians tend to balme AirBnB and real estate investors and they all focus on some kind of market regulation. Mostly just talking about it because they know any strict regulation would be unconstitutional. From the technical perspective the solution is simple. We should just build more houses in big projects like we did 40 years ago which will drive down the unit price and also provide all the necessary infrastructure like public transport and schools. Pretty big portion (tens of percent) of Prague's housing capacity was build during the 40 years communist era. If we could successfully build huge housing projects like Jižní Město (https://en.wikipedia.org/wiki/Ji%C5%BEn%C3%AD_M%C4%9Bsto) during this awful regime whit very limited economic resources then it's surely doable now and in much higher standard. We just lack the political will to think longer then next 4 years till the next elections and to solve the problems instead of just talking about it and blaming someone else.