>I heard that Germany has a good 'social protection' too - but I heard that also a long time ago

well, fortunately this still applies to Germany!

Here in Germany, in a normal case, every employee has a contract.
If the contract doesn't include a period of cancellation, both sides need to notify at least 4 weeks before the end of the month.
Common cancellation periods for contracts are "6 weeks before the end of a quarter" or "3 months to the end of a month" or "6 months to the end of a month". In all cases, the employer needs a valid reason for firing the employee. The employee does not, if he wants to leave.
Sometimes, employers try to prevent employees from working for a competitor in the same business after they have left, but thats illegal.