cumulative translation adjustment (CTA) as double entry

In essence, you ARE making a double entry (you have to be or you BS won't balance). Think about the absolute simplest case. You put 1,000 into a foreign currency entity when the exchange rate is 1:1. So in your Foreign Currency entity, you have 1,000 cash and 1,000 equity. If you translated to your reporting currency at that very instant, it would also be 1,000 cash and 1,000 equity. A month later, the rate is now 2:1, so when you translate the cash, you now have 2,000 in your reporting currency (spot rate), but 1,000 equity (historical rate). You "plug" the 1,000 to CTA, but in fact, you already made one side of the entry by increasing your cash balance from 1,000 to 2,000. A good FAS 52 model (sorry, I still use the old references) will track your CTA by each asset/liability so you can release the CTA as necessary.

2