There are categories for the level of difficulty for each language according to the State dept, the fifth level for example is for the most difficult ones: Ara

There are categories for the level of difficulty for each language according to the State dept, the fifth level for example is for the most difficult ones: Arabic (Levantine, Iraqi), Chinese, Japanese, Korean, Pashto- you will need 64 weeks, while for French, Italian, Portuguese, and Spanish 26 weeks will do.