There is no definitive answer to which language is the toughest in the world as this will vary depending on the individual and the level of complexity that they find difficult. However, some languages are known to be particularly challenging such as Chinese, Japanese, Korean, Arabic, and Russian. These languages require extensive study and practice, as well as a thorough understanding of the cultural and historical context that the language exists in. With that being said, anyone wishing to learn one of these languages must be prepared for a difficult, but rewarding, journey!