Final answer:
Nicaragua is the country with the Mosquito Coast and shares the Gulf of Fonseca with El Salvador and Honduras.
Step-by-step explanation:
The country that has the Mosquito Coast and shares the Gulf of Fonseca with El Salvador and Honduras is Nicaragua. The Mosquito Coast is located on the eastern coast of Nicaragua along the Caribbean Sea. The Gulf of Fonseca is a Pacific Ocean inlet that forms part of the border between Nicaragua, Honduras, and El Salvador.
While the Gulf of Tehuantepec is in southern Mexico, and references to other countries such as Costa Rica, Guatemala, and Belize relate to the broader region of Mesoamerica, it is Nicaragua that is relevant to the Mosquito Coast and the Gulf of Fonseca.