When it is seen to have risen too far, the central banks of major countries cooperate to intervene.
サミットって、主要国首脳会議のことなんですか?
By summit, do you mean the Group of Eight?
米国通貨を大量に売っている投機筋に対抗して、主要国の中央銀行は市場で大規模な協調介入を行った。
In a fight against speculators who are dumping the U.S. currency, central banks of major countries have carried out massive concerted interventions in the market.