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How to trade “exotic” currencies?
Use a currency ETF.  there are many.  Specific to your question there is WisdomTree Dreyfus Brazilian Real Fund (BZF) I don't happen to find a currency ETF for Thailand, so the closest you could come to a Thai currency fund would be something that's an Index fund ETF that is based on an index in the Thai Market such as:  MSCI Thailand Investable Market Index Fund Because that fund is investing in an index of stocks that trade on the Thai market, you are in effect investing in something denominated in Baht.  This is spelled out in the prospectus where it discusses 'currency risk'.   The problem is that you are however not investing in just the currency, but rather a broad index of stocks denominated in that currency.  Still to the extent the market holds fairly steady, you get much the same effect of investing in just the currency.  to the extent the market is moving, you get the net effect of what the thai market does, plus how the bhat trades relative to the dollar.