US manipulated usdx by doing QE, BOJ manipulates jpy by selling joy.. usdjpy below 80 was breaking point look at charts and what they said. SNB said 1.2 eurchf and intervened.. the guys wife bought shitload of EUR and sold CHF prior to the big billion EUR order. Australian bank has been talking down AUD by saying its too high around 1.07.. and it fell.. and im guessing NZ central bank is doing the same... selling NZD because its a race to the bottom for exporting countries.
Central banks do let their currencies fluctuate somewhat (even china allows their currency to move up and down by a small amount every day). The issue comes when a currency moves in one direction too far, threatening the economy if intervention does not occur
Intervention always ends up hurting more than it helps... it fakes demand similar to QE and all other forms of manipulation... it will come back to bite. If it moved up too far or down too far.. tough loss your decision to sign plaza accord creating a deflationary spiral for everyone else other than USD.