Full credit is granted for all withholding tax deducted

Foreign withholding taxes on income from abroad are
usually credited against the applicable German income tax, unless the relevant
tax treaty specifies otherwise. Employment income taxable abroad is often
exempt from further German taxation in the hands of a German resident, while
most treaties declare a German resident’s foreign investment income to be
taxable in Germany but allow a credit for the foreign withholding tax actually
paid.

No credit is given for underlying income or corporation tax and any
unused foreign tax credit can be neither carried forward, nor applied against the
tax on domestic-source or third-country income.