If you're thinking about taking up Mandarin, you better have 2,200 hours to spare.
The Foreign Service Institute of the U.S. Department of State compiled learning expectations for native English speakers looking to achieve speaking and reading proficiency in a number of different foreign languages, based on factors including the complexity of the language, resources available, how many hours devoted to study each week, and student motivation.
Voxy.com put together this nifty infographic (via The Cultureist), broken down into easy, medium and hard language categories.
The easiest languages - including Spanish, French, Portuguese and Italian - require just 23-24 weeks of study, or 575-600 class hours, to achieve proficiency, and are the easiest because of their closeness to English.
The most difficult languages - Arabic, Chinese, Korean and Japanese - require, on average, 1.69 years (88 weeks), or 2,200 class hours, to reach speaking and reading proficiency.
Each of the four "hard" languages is difficult for its own reasons. Arabic's lack of vowels makes reading difficult for an English-speaking native, while Japanese and Chinese require the memorization of over a thousand unique characters.