French

English borrowed roughly 29% of its vocabulary from French after the Norman Conquest of 1066 — words like "restaurant," "entrepreneur," "cliche," and "regime" are already in your vocabulary. The FSI rates French at 600 hours. The main difficulty is pronunciation: nasal vowels, silent final consonants, and liaison (linking words together) make spoken French significantly harder than written French. But French is spoken across 29 countries on five continents, making it one of the most geographically useful languages on Earth.