The official tourism board for Belize is http://www.travelbelize.org/ .  It’s available in English, Deutsch, Español, and Japanese. 

 Two more helpful websites for planning your trip are http://ambergriscaye.com and http://www.belizeforum.com/ which are not official tourism sites but message boards frequented by locals and frequent visitors.  The Ambergris Caye one receives more traffic but both will provide a wealth of information by first using the search function for topics covered often and then posting which will often receive answers within minutes.