I think that the field is fraught with a number of caveats, just off the top of my head: * "I learned a language" is a very poorly defined statement. It's real

I think that the field is fraught with a number of caveats, just off the top of my head: * "I learned a language" is a very poorly defined statement. It's really difficult to quantify. The EU tried with their language levels [1], but it's still a mess. So you get a person that says "I speak 15 languages! Just follow my method forehead!" while an academic says "this person speaks two languages barely, and makes noises in the rest." "I know a language" means different things for different people, depending on one's motivation to learn a language. Do you want to book a hotel room? Do you want to read a newspaper? Do you want to read Crime and Punishment in the original? Note that, for example, reading a newspaper is significantly easier in Tagalog, which uses a mixture of English and Filipino, than in Chinese, which requires you to know around 3 thousand Chinese characters. * Learning a language is highly influenced by your native language. If you take 20 undergrads, you might conclude that "to learn language X as a native speaker of Y, the best method seems to be Z." Then, other papers will likely dispute your definition of "learning" (see previous point). * Learning a language is highly dependent on your motivation. If you take a class of 20 people, their motivation to learn a language X is going to be all over the place. Learning a language is always really difficult, even when a language is deemed easy (like Spanish). Most people will drop off unless they are really driven to learn the language. Long story short, I don't think it's as easy to apply the scientific method. There's a reason why we don't have a matrix of "if you're a German speaker wanting to learn Russian, here's the optimal syllabus for you." On the flip side, I do think we can say something about language learning. For example, apps like Duolingo are not that useful. I don't think that's a very controversial statement in the language learning community. Similarly, just moving to a country won't do anything special for you (other than utterly isolate you). For example, you won't pick up any Japanese from your one-room 40-squared-feet apartment in downtown Tokyo alone. [1] https://en.wikipedia.org/wiki/Common_European_Framework_of_Reference_for_Languages#Common_reference_levels https://en.wikipedia.org/wiki/Common_European_Framework_of_R...