I am looking for a public-domain questionnaire asking for drug
side-effects in either English or German or any other main language

Not sure of your context, but in clinical trials it's considered poor
practice to prompt volunteers with questions about specific types of
event. Generally questions such as "Have you experienced any unwanted
effects over the past nnn days?" are used.  If you start asking "Have
you had a headache? Have you had a rash?", false memory will draw more
responses than are plausible.