Methods for discovering which language is the hardest to learn
Languages differ in how hard they are to learn, they are not just 'different' or some other relativistic nonsense. Aside from intuitve estimates, is there some systematic way to measure how hard a language is to learn? The answer is “yes”. The first time i talked about with this another person, i was amazed to hear that he thought it was impossible to rank languages in order of difficulty to learn, even conceptually. I can think of a number of ways to figure this out, some better than others.
Clarifying the question
But first it is a good idea to clarify exactly what we mean by “the hardest language to learn”. Are we talking about learning it as a native or a foreign language? I want to include both, but it is possible to separate them if one so wants.
Method 1: the National Virtual Translation Center-inspired method
The US collects data about how many weeks of training one needs to learn a foreign language good enough for working on an embassy in the country where it is spoken. The idea is simply that one can collect data like this for all other language combinations (or the ones we're interesting in, anyway), and see which languages often end up in the “takes a long time” category etc.
If they do not teach the language to a particular skill level but just give people a course that takes the same amount of time, one can still use this method altho slightly modified. One can test these students after they have completed their training and see how good they are at the language. The better they are, the easier the language is to learn.
Method 2: Comparing the students of two languages learning each other's language
For every two given languages, there are students that have the first or the second as their native language and is learning the other one. One can measure how good these students are at the language they are learning. One will need to correct for exposure to the language outside class, which is mostly a problem with english since it is the world language, but otherwise not generally a problem.
Method 3: Asking students of two languages learning each other's language
Similar to the second method, one can ask these students which language they think is the hardest to learn: their native one or the one they are currently learning. I wud think that this wud point in the correct direction, even tho the native language has a bias in its favor (becus of earlier exposure). Still, for the easier languages, one will see more people responding that they think that the foreign language is easier.
The best thing about this method is that it is relatively easy to do and costs virtually no money. One can even do it with surveys on the internet. One will need a huge amount of data to draw conclusions, and obviously such data will be missing on smaller languages, but the largest, say 20 languages, in the world shud be easy to rank according to the data.
Method 4: carefully analyzed expert opinion
The idea is to use the same method as used in this paper1 to judge various languages about various things in them, such as writing script, fonology, (foneticness of the) orthografy, grammar (grammatical gender, inflections, etc.) and probably some other things i havent thought of. The method is designed to reduce bias and prejudice. This wud probably give some results that are close to truth.
1 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2810%2961462-6/abstract -Drug harms in the UK a multicriteria decision analysis