When did the allies transition from fighting a defensive war in the pacific to going on the offensive against

 June, 1942 after America won the Battle of Midway (June 4 - 7 1942) 

Currently, as of february 2016, an american traveling in france would be by the exchange rate. the weakness of the euro and the strength of the us dollar means that items in france cost less to an american than they otherwise would. of course, if this trend reverses and the us dollar weakens and the euro strengthens, such as was happening in early 2008, an american traveling in france would have an adverse experience because items would cost relatively more.