Sorry if I scared you. But you will struggle anytime you don't speak the native language. Thankfully, in tourist markets, people need to speak multiple languages. Just expect to pay for the service. I personally have never flown into Nicaragua. I have traveled through it by car when I helped somebody drive a car from the states. Yes, I speak fluent Spanish. To me it's indispensible. I personally wouldn't imagine trying to get from the airport to some bus terminal in downtown Managua that takes me to SJDS without being Spanish fluent....but shit it can be done. Perhaps the Airport has a TicaBus/TransNica terminal. Can't help you there. I'd bite the bullet and pay a shuttle directly....unless you want the experience, then go for it bro.
Here is a shuttle that charges $40 directly for one person. If you aren't going alone, it gets cheaper. I guess the logical question is how much do you want to pay?