Hi Stepan!
Yes, Sweden is wonderful in summer with the long nights. I was last there in late June, just after mid-summer, and it never really got dark, just a sort of deep twilight. I was fascinated, as previously I had only been there in winter. I was trying to remember the name of the boats used for the tours of the canals in Göteborg, and I think they are called "padan"...am I correct? I also liked the "fish church" and the fish, which was most delicious.
Believe it or not, I have only been to Berlin once, but it is a fantastic city with a great atmosphere and such a lot of history. In character it is totally different to Stuttgart (or at least I think so).
GREENOWL