What should I do if my department head encourages us to do questionable practices to raise publication indices?
This is scientific misconduct. First, you are responsible for yourself. In your situation I would not follow these practices since it can (and probably will) have bad consequences for you.

However, you should address your concerns. Almost every university has a person who is responsible for scientific integrity. Sometimes he/she is called ombudsman. Have a talk with them. Try to do this in an anonymous way, otherwise I would fear the consequences.