All of our prices are shown in US dollars, and all of our transactions are done using USD.
However, you should still be able to pay for a Leanpub purchase with your credit card, even if your local currency is not US dollars; we sell ebooks to people all around the world every day.
(However, please note that in some cases your financial institution may charge you an extra fee for a currency exchange rate, or a related fee; we have no control over this ourselves.)