I found in various online dictionaries the French translations for the English "currency" either to be "la monnaie" or "la devise" (among others, but these seem to be the most prominent). Are both exchangable? Or is there any important difference?
Currency as "monnaie" is a monetary unit used in your own country while currency as "une devise" is a monetary unit which can be used for international exchanges. This implies that all "devises" are "monnaies" but not every "monnaies" are accepted as "devises".
"Une devise" can be converted in another "devise" while it's not true for every "monnaies".
Bonus: "Monnaie" is something you use in your everyday life : "I'd like to buy a coffee, do you have some "monnaie" left ?". "La petite monnaie" usually refers to coins.