[fabianholzer]

The standard in Germany is put down in the civil code (Bürgerliches Gesetzbuch) as four weeks to the 15th or the end of a month. That means when you have a working contract which doesn't specify explicitly something else, it automatically applies as put down in the BGB. Still, it is perfectly legal (and also not unusual) to have longer periods. Anyway, it is still a market economy and contracts are negotiated between (in legal theory at least) two equal parties.