Which language had the biggestn impact on human history?

Depends on one's criterion. Today, English is the most important language, but there was a time when Spanish was a fair contender. French was once considered the language of diplomacy and Latin, of course, was the language of science and religion, at least in the West, whereas Greek fulled that role in the East of Europe. Though of comparatively limited speakers, Hebrew has been significant through religion and the descendents of Sanskrit have had vast, if underappreciated, effect. Chinese and Arabic may become more important in the future.