Final answer:
Henry Wadsworth Longfellow is the Fireside poet whose work was widely translated and read internationally.
Step-by-step explanation:
The Fireside poet whose work was translated into a dozen languages and read by millions is Henry Wadsworth Longfellow. Longfellow was one of the most popular American poets of the 19th century and his works, which include 'The Song of Hiawatha' and 'Paul Revere's Ride', resonated with both American and international audiences. His poetry's themes of American history, mythology, and cultural identity contributed to his widespread appeal and translation into many languages.