It is illegal but common practice.

Depends on the business. We’ve got a ridiculous minimum wage of 13,90€ . Most honest restaurant collect the tips and split them, so even the cooking staff receives something.

For employees the tip is tax free. Businesses owner have to pay taxes.

With the most tips being payed via card (10-25% preselectable), I doubt that the staff sees any of it.

Every European country has its own valid culture of tipping. Some consider tipping unfriendly or even hostile.

In Germany you used to gratify a special service or outstanding servers.

Sadly this gets americanized already.