The most spoken language in Nicaragua is Spanish, spoken by 95% of the population. If you go to the Atlantic Coast, you will find some other languages in different communities, like Garifuna, Miskito and Nicaragua Creole English.
If you only speak English and plan to live in Nicaragua full time, we do encourage that you learn the basics of the language to get around. Nicaraguans are very helpful and willing to assist you if we see a foreigner in trouble or needing our help. However it's always good when you know at least the basics of the language in case you are in a remote village or main road and no one speaks English.
Many people who has retired or moved to Nicaragua for their businesses have come without knowing one word of Spanish, and after a month or two, they know the basics and have learned more than they ever thought they would.
Nowadays, more and more Nicaraguans are learning English too, so in Managua, you will now find English speaking people working in stores, supermarkets, banks, and restaurants, so it's getting easier for foreigners to live here.