In principle, your employer must approve your vacation application. Also look at the rules that apply at your employer. Your employer may only reject your vacation application if your business is endangered by your absence. If this is the case, your employer must let you know in writing within 2 weeks. If this does not happen within 2 weeks, your holiday application has in principle been approved.
Always check your collective labor agreement to see if different agreements have been made about this. Furthermore, you must of course still have sufficient vacation days.