Method and Conclusion. See here.
Results. A ratings system was designed in terms of how difficult it would be for an English-language speaker to learn the language. In the case of English, English was judged according to how hard it would be for a non-English speaker to learn the language. Speaking, reading and writing were all considered.
Ratings: Languages are rated 1-6, easiest to hardest. 1 = easiest, 2 = moderately easy to average, 3 = average to moderately difficult, 4 = very difficult, 5 = extremely difficult, 6 = most difficult of all. Ratings are impressionistic.
Time needed. Time needed for an English language speaker to learn the language “reasonably well”: Level 1 languages = 3 months-1 year. Level 2 languages = 6 months-1 year. Level 3 languages = 1-2 years. Level 4 languages = 2 years. Level 5 languages = 3-4 years, but some may take longer. Level 6 languages = more than 4 years.
This post will look at the Southern Nambikwaran language in terms of how difficult it would be for an English speaker to learn it.
This is actually a series of closely related languages as opposed to one language, but the Southern Nambikwara language is the most well-known of the family, with 1,200 speakers in the Brazilian Amazon.
Phonology is complex. Consonants distinguish between aspirated, plain and glottalized, common in the Americas. There are strange sounds like prestopped nasals and glottalized fricatives. There are three different tones. All vowels except one have nasal, creaky-voiced and nasal-creaky counterparts, for a total of 19 vowels.
The grammar is polysynthetic with a complex evidential system.
Reportedly, Nambikwaran children do not pick up the language fully until age 10 or so, one of the latest recorded ages for full competence. Nambikwara is sometimes said to be the hardest language on Earth to learn, but it has some competition.
Southern Nambikwara definitely gets a 6 rating, hardest of all!