Re: Losing deposit on apt in Berlin: allowed someone stay there rent free - sublettin
Attitudes to subletting differ in various places. Many Irish landlords relaxed about.
In the USA some states have local byelaws against overcrowding which are strictly enforced.
Don't know about Germany. As one poster has already suggested the German Embassy there have a list of English speaking lawyers. From previous experience of Germans they tend to have written agreements for most situations, keep to them themselves and expect you to keep to them.