score:6
No, you don't need local currency. Istanbul AtatΓΌrk is a massive transit airport (>50m passengers in 2013), and virtually all shops are more than happy to accept credit cards. Some will even take euros, but the exchange rate will not be in your favor.
Upvote:5
In the transit zone, shops will accept credit cards and cash in a lot of different currencies:
I have also found at least one ATM where I could retrieve TRL and EUR with my Maestro debit card. This is useful if you need Visa to enter Turkey, because it can only be paid with USD or EUR, not TRL !