I'm a bit disheartened that Korean is in group 4. T__T
The US Foreign Service Institute (FSI) divides languages into four tiers of difficulty for native English speakers to learn. Group 1, the easiest of the bunch, includes French, German, Indonesian, Italian, Portuguese, Romanian, Spanish and Swahili. According to FSI research, it takes around 480 hours of practice to reach basic fluency in all Group 1 languages.
The difficulty begins to spike as we move down the list. It takes 720 hours to achieve the same level of fluency in Group 2 languages, which include Bulgarian, Burmese, Greek, Hindi, Persian and Urdu. More difficult are Amharic, Cambodian, Czech, Finnish and Hebrew, which places them in in Group 3. Group 4 is comprised of some of the most challenging languages for English speakers to grasp: Arabic, Chinese, Japanese and Korean.