I have 2 iTunes accounts. One account is German and uses a credit card with a German billing address. The other account is U.S. and uses a credit card with a U.S. billing address. I can purchase from the German iTunes/App stores while in the U.S. and I can purchase from the U.S. iTunes/App stores while in Germany. If you want to use only one account and switch countries in that account, you will need to use a credit card with a billing address in that country. I didn't want to switch countries and cards in the same account all the time, so I made a 2nd account and don't need to switch anything.
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