Foreign Service Institute language difficulty rankings are an indication of how long a native English speaker would need to reach proficiency in a number of different languages.
There are five categories, ranked from easiest to the hardest based on how many classroom hours a learner would need to reach professional working proficiency (i.e. Level 3 on the Interagency Language Roundtable scale).
Foreign Service Institute language difficulty rankings
The below language difficulty chart is based on the FSI language difficulty ranking at US State Department.
See also: What are the hardest languages to learn?
Category I: 23-24 weeks (575-600 hours)
Languages closely related to English
Category II: 30 weeks (750 hours)
Languages similar to English
Category III: 36 weeks (900 hours)
Languages with linguistic and/or cultural differences from English
Category IV: 44 weeks (1100 hours)
Languages with significant linguistic and/or cultural differences from English
Persian (Dari, Farsi, Tajik)
Category V: 88 weeks (2200 hours)
Languages which are exceptionally difficult for native English speakers
* Usually more difficult than other languages in the same category.
The data is sourced from the Foreign Service Institute Language Difficulty (FSI) at the US Department of State.