The dress code in Nicaragua is very casual. However the dress code will always depend on the purpose of your visit and the time of the year you are coming.
If you are planning a vacation trip to Nicaragua, and you are a man, you can wear khaki pants, black pants, or jeans, with t-shirts or very lightweight shirts. You can wear your tennis shoes, sandals or even flip flops unless you are planning to explore the mountains, for which we strongly suggest to have jeans and long sleeve T-shirts, with either boots or sneakers. If you are a woman, you can wear shorts or jeans with t-shirts or buttoned shirts, or dresses, flip-flops, sandals, tennis shoes.
Don't forget to bring your swimsuit, sunglasses and a hat, and keep your sunscreen and bug spray handy.
If you are planning to live in Nicaragua full time, I would encourage that you have a little bit of everything in your closet, because I'm sure you will make a lot of friends and have many social events where you will have to wear more dressy clothes. Nicaraguans are very social and tend to make family reunions very often.
If you plan to visit during rainy season, just bring your raincoat and jeans. October is when we get most of the rain in Nicaragua.
Nicaraguans don't tend to wear suits and ties, unless it's a wedding, or a very formal business meeting. You can always wear buttoned shirts long / short sleeves and slacks. Women will always looks great with a nice dress.
Nicaragua is a very relaxing, adventurous, full of activities country. Make sure to do some research about the places you want to visit, to make sure you have the right outfit for it.