In order to configure different public holidays for your employees, you should create different holiday calendars. Go to Configuration -> Holidays and choose "Manage" on the calendars list.
For each country you need to add a new holiday calendar. Then you will be able to assign a calendar to an employee.
The third step is to add new holidays to the calendar. In order to do that, open Configuration -> Holidays -> Choose the proper calendar from the dropdown. You can add holiday one by one or import them from the list suggested by Google.
After adding public holidays to each calendar you are able to assign a calendar to an employee. In order to do that, open Configuration -> Employees and edit a chosen employee. In the next step just choose the new holiday calendar from the list.