Request Colleges internationally to let students participate in a survey
In many places (say, the US), there are laws that govern any sort of research with human subjects. This applies even to questionnaires. These laws differ widely from place to place and it is even possible that asking a question in some other country Y might have issues. 

In the United States, universities have an IRB (Institutional Review Board) which will look at what you want to do and approve it or make suggestions about how to improve it within the law and ethical regulations. 

Germany may well have similar laws and regulations. 

Wherever you are, look to an IRB or a Research Office to obtain valid feedback on your plans. This will, perhaps, ease your approach to universities in other countries to obtain permission for your questionnaire.