If you want to be a local then wear jeans regardless of how warm it is, never cease to amaze me, I'll be out in shorts sandles and armless Tshrit and I'll see people wearing jeans and jackets out. Maybe they're used to heat I don't know but I rarely see people wearing shorts, tank tops yes, but shorts no.
A little aside Germany the fastion is 3/4 pants shorts are only for sports. Then its much cooler there.
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Be Canadian Eh, that's for all you American out there:)