In some Google services the payment may be carried out not in the currency of your home country. If possible, Google will charge you in your local currency. Google gets this information from the home address that you added in your Google Wallet account. If that isn't possible, you'll be charged in a different currency that is usually U.S. dollars outside the United States. You'll always see the currency you'll be charged in before you complete the transaction.
See here for the source of information as well as for more details on changing the profile data and currency conversions.
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