According to Economic Confidential blog " IMF says, Crypto Assets May Displace Local Currencies in Developing Countries". Source: Economic Confidential, Facebook page..
Bitcoin is taking over the internet for online transaction, therefore, most of the local currencies in the developing Nations are affected.. because developing Nations are not inclined in the e-currency transaction while the new generation youths use the e-currency for transactions. That making the local currency weak.
Can Bitcoin really weaken the Local Currencies in the Developing Nations?
Actually, think no, bitcoin can not weaken the local currency completely. Both bitcoin and local currencies has a great role to play in the economic development of the nation, bitcoin gives some influence to the local currency because some time the price of bitcoin in the market have effect to some local currency values, but government may not allow bitcoin to have the overall control over the local currency, so it's not possible for developing countries local currency to be over powered by bitcoin.