Street-theatre festivals in Germany:

Berlin lacht

Straßentheater Holzminden

Just for Fun Darmstadt

Welttheater der Straße Schwerte

Internationales Straßentheaterfestival Ludwigshafen

ViaThea Görlitz

tête-à-tête Rastatt

Other street-theatre festivals:

Poland
International Street and Open-Air Theatres Festival FETA 

Belgium
MiramirO
 

Other events in Detmold:

Detmold Summer Stage

Smaller Events in Detmold