Some things about Chinese are hard, some are easy. The Defense Language Institute in Monterey, California, divides the languages they teach into four groups, from easiest to most difficult, as measured by the number of hours of instruction required to bring students to a certain level of proficiency.

For more information, please check http://www-personal.umich.edu/~wbaxter/howhard.html

PDF file and website link were provided by Robin Workman.