Local vs. foreign currency denomination for Emerging Market Bonds
An EME's government collects taxes in domestic currency. If it issues debt in foreign currency and the domestic currency depreciates, the value of foreign currency-denominated debt increases. For example 1 000 000 000 USD is due at some date. If the exchange rate is 1 peso per dollar the government has to collect 1 000 000 000 pesos to pay it off. If the exchange rate becomes 1.25 pesos per dollar the domestc government has to collect 1 250 000 000 pesos. If the debt was denominated in pesos all along the government would still need only 1 000 000 000 pesos. 

If debt to GDP is high such a depreciation may cause the EME government to default.