St. Barths and Belize? I don't think you could pick two more different places in the Caribbean Basin!
St. Barths is French-speaking, with a truly French je ne sais quoi, the most expensive island in the Caribbean. The emphasis is on fine cuisine, good wine, French culture, beautiful people, private villas and ultra expensive hotels, beaches and la vie en rose.
Belize is English (and Spanish) speaking, with a British heritage, friendly, laid-back, rainforests, ruins and rum.