Taxes in Croatia

not sure about taxes, but i know that sales takes is around 23%.
Is that 1000 Euro a month?

WHAT ?

the Porez na dodanu vrijednost is 23%, sorry not 24%. But as a foreigner you can fill out a duty free form at the airport  once you arrive and that way you don't have to pay the PDV.  Some stores accept the duty free form and others dont.  If they don't accept it then when you leave the country you would get your money back that you paid.  But not sure if this rule applies if you are working there. 
Why croatia?

my girlfriend leaves there

but i didn't find anything so i will try to go to germany

VAT in Croatia is 25% but for income taxes are working differently.

http://www.moj-posao.net/Kalkulator-Placa/

This online calculator can give you an idea about your net or gross salary.
You can pick if you want Net->Gross or Gross->Net calculation.
Salaries in Croatia are negotiated in net amount, but maybe there might be exceptions for foreign employees.

Terms used in calculator:
Iznos - Amount
Mjesto prebivališta (prirez) - Location, local taxes are different
Broj djece - Number of children in household
Broj uzdržavanih osoba - Number of dependent persons in household

Bez invaliditeta - no disability
Djelomična invalidnost - partial disability
100% invalidnost - 100% disability

After you pick your option for calculation you get specifics on how much money is going for retirement fund, taxes and health insurance.

thank you