Your Yotta debit card can be used anywhere that MasterCard is accepted. While Yotta doesn't charge any international fees, the merchant or MasterCard may charge conversion or other fees.
There are some countries where you won't be able to use your debit card at ATMs or with merchants, and the card transactions will decline:
Albania
Balkans (excluding Bulgaria and Romania)
Belarus
Burundi
Bosnia and Herzegovina
Central African Republic
Cuba
Democratic People's Republic of Korea (a.k.a. North Korea)
Democratic Republic of Congo
Estonia
Iran
Iraq
Lebanon
Liberia
Libya
Mali
Malta
Myanmar
Nicaragua
Nigeria
Pakistan
Russian Federation
Somalia
South Sudan
Sudan
Syria
Turkey
Ukraine
United Arab Emirates
Venezuela
Yemen
Zimbabwe