No, but it does help! On each of our builds we will always have local translators available, and we do our best to give our volunteers many opportunities to communicate with the people that they are working with.
In the Dominican Republic and Mexico the official language is Spanish. In Haiti, they speak creole, which is a French/African-based language, there are also Haitian communities within the Dominican Republic that speak creole as well. If you speak French, you will be able to communicate fairly well with Haitians! For Thailand, it’s Thai!
It’s always great to brush up on some useful phrases in the language of the country you are visiting.