There are two methods to avoid the double taxation, the exemption method and credit method. The exemption method is common between western countries that do not have a large difference in their tax rates. The individual pays German taxes only for the German income. The credit method is common with countries where the tax rate is a lot lower than in Germany (e. g. Middle Eastern and Asian countries). In these cases, the individual pays taxes in Germany for his world income and receives a credit for the foreign taxes paid.
If you speak German please also visit my German homepage by clicking here.
Please contact me if I may give you further explanations.