It is not the governments job to maintain the value of our currency so expats don't have financial problems. There are some good economic reasons for keeping the value of a currency low, since it tends to increase exports. That's why China has been resisting floating its undervalued currency for so long and had to be pressured into the minimal changes it now allows.

It's difficult, too, to determine what part of the dollar's losses are caused by US actions, and what part is caused by China's newly powerful economic position and the strength of other economies, so even if you sued, how much could you sue for?

Countries do not have total control over the value of their currencies unless they choose to peg them. That is a very expensive, as the government frequently has to spend a lot of money to prop up the currency. That's why so many countries have let their currencies float freely in recent years. The Malaysian government used to peg the ringgit within a very tight range, but fairly recently decided they had to let if float.

I agree with Steve, it's a risk you take when you move. Some people make out with currency fluctuations. Expats in Argentina a few years ago suddenly found that they had four times as much money when the Argentinian currency collapsed.

It's hard, though, to imagine how big the impact can be. Inflation is very low in the US, yet at an average of 3%, the dollar will lose half of its purchasing power in (72/3) 24 years. It's worse for people on social security, since a different inflation rate (the core rate) is used to for adjustments. The core rate doesn't include gasoline prices.