Native English speakers traveling to Belize will have no problem communicating, as the official language is English. Spanish is also widely spoken, especially in the North and West of Belize.
Most Belizeans can understand Creole, which is a type of pidgin English. However, for the visitor who decides to hop across Belize's borders with Mexico and Guatemala, fluency in languages will be tested – it's suddenly Spanish all the way.
It's always good to have some fluency in a foreign language when traveling!