Just in case it matters to anyone...
No, I do not have a degree in linguistics, nor have I studied linguistics extensively.

The reason is that linguistics does not address the issue that is most relevant to me:
"What is the most effective way (for an adult) to learn another language?"

The other reason is that most research papers are so arcane and densely written that they're impossible to understand. There are a few exceptions (e.g. Stephen Krashen).

For those of you who'd like to learn Thai, be thankful that I did not study linguistics. The "linguistics" approach is how most languages are taught and it's unnecessarily complicated. I worked really hard to learn German at school and got nowhere (there were too many words, too many declination tables, too many irregular verbs, each with their own conjugation tables, etc.) But if you learn German using the Rapid Method, it's actually a very easy language.

In order to learn a language you need to do the following:

  1. Train your mouth muscles to produce the sounds automatically (like a golf or tennis swing) - I call this Developing Muscle Memory. The way to do this, in a nutshell, is to take a word or phrase or sentence and practice saying it clearly in an exaggerated way over and over again until you can do so quickly and accurately.

  2. Learn to read so that you can absorb the language from your environment.

    This is a real challenge for languages like Chinese or Japanese. As an interim measure, you will need to learn the phonetic alphabet in parallel: pinyin (or preferably zhuyin) for Chinese, or hiragana & katakana for Japanese, because many readers for native speakers will provide these to help you decipher the more difficult or uncommon characters.

    I considered learning the IPA in order to study Chinese, but I found that nearly all the learning material (and children's books) and even the way you create the characters on the keyboard is done in pinyin. Every Japanese who uses a computer or smartphone (i.e. everybody) types in "romanji", so you can probably get by for a long time without knowing how to read in Japan. Nevertheless, there is nothing more frustrating and demoralizing than to wander about a Chinese or Japanese town and have no clue what the street signs & notices mean, not to be able to understand a single menu and never be able to progress your language ability by dipping into a novel or magazine article.

  3. Memorize the high-frequency words used in conversation. Focus on informal conversation in the beginning unless you are only going to spend your time with professionals in a polite business setting. You want to make friends and you want to talk to your friends. The politer, more formal ways of speaking can come later.

    There have been several analyses of language usage which show some misleading statistics, such as the top 100 words are used 50% of the time. You should obviously learn these 100 words, but you will anyway without any special effort because they are so frequent. It won't help you understand anything, however.

    The top 500 words make up 70% of language usage. Yes, you need to know these words. So your first step is to memorize them as quickly as possible.

    However, 70% is not nearly enough. You need a minimum of around 1200 words just to be able to get by in everyday interactions like ordering food, shopping, greeting people, traveling around, etc.

    It's still not enough to have a conversation with anyone. 1200 words is 80% and that means you can't understand every fifth word in a conversation and will struggle to express even the simplest ideas.

    You need another 1200 words or so to be hold a rudimentary conversation, but preferably a good 3000 words altogether (95%) to be able to start expressing and understanding conversations about everyday matters.

  4. Don't study phrases. Study sentence and phrase patterns. You don't need to understand the grammatical reasons behind the various patterns, but you do need to know what are the patterns to use for each situation or idea you'd like to express.

    Once you've learnt and practiced all the relevant patterns, all you need to do is slot in the appropriate word(s).

    There will obviously be quite a lot of patterns to learn. What I like so much about the Everyday Thai for Beginners course is that Khun Wiworn has covered all the essential patterns, in a logical and fairly well-connected progression, that you need to know in order to get around in Thailand. There are a few hundred patterns to learn, so it won't take long. Better than trying to memorize a grammar book with perhaps over a thousand rules that are usually arranged by function linguistically rather than "what do I need to know and how do I express myself in this particular situation?".

  5. It's important to select the right words and material to study and memorize. As a beginner, you want to focus on words used in everyday conversation, not books - and especially not school material.

    That's why, even though the Rapid Method focuses on reading, it's vitally important to read spoken material, not literary texts. Otherwise you'll be like my friend who could devour books by Voltaire and Hugo and Camus, but couldn't talk to a single French person other than the waiters in a restaurant.

    I had a similar problem as a consultant. I conducted regular meetings in French with European politicians about strategy and policy and implementation issues, but I couldn't understand a word of what my French colleagues and friends were saying in the pub or at a party.

  6. Therefore, you need to study vocabulary that is relevant to how you will communicate in the language. For most expats, this means a functional vocabulary for getting around and buying things, plus a vocabulary for conversing with friends and lovers. If you are working or in business then you need a different vocabulary; and obviously there will be some overlap. If you intend to read (or write) formal documents or literary texts then you will need a completely different vocabulary set.

    Most people start by learning the vocabulary they need to communicate in class - which unfortunately isn't particularly useful out on the street or when talking to friends.

    In general, the most effective way to learn a language is to break it up into "zones". Learn - and master - the language of each respective zone. Choose just the zones that are relevant to you and ignore the rest. Don't bother with writing, for instance. It's a special, more formalized version of the language.

    For most people, the first zone to focus on is "getting about" (greeting people, asking for directions, thanking them, ordering food, buying things, etc.)

    Then you'll want a "social zone": to be able to make friends and will probably end up in a relationship with someone (or at least want to talk to people about their spouses/lovers/family/etc.).

    You might not care much about the "commercial" zone. There will be other zones that are relevant to you: "building & construction", "school and education", "news and media", "politics", "religion" and eventually "medical", "academic", "literary" and "science" zones, etc. Each of these zones have their own unique vocabulary set (with some overlap) and ways of expressing ideas. Even in one's own language, you need to learn the jargon if you want to talk about a particular topic. If I want my car fixed, not only should I know some of the terminology for things like spark plugs and carburetors, but also the idiomatic ways to describe problems ("the engine is not running smoothly", "there's a knocking sound", "the clutch sticks"...)

    Being selective in what you study is the secret to making good progress and learning efficiently.

  7. Use mnemonics and spaced-repetition to memorize words and patterns and rules.

    This is vital. You need to "do the time" in order to be able to communicate. But it's no good just understanding the mechanics of how to put sentences together, it all has to be internalized and immediately-accessible in your mind.

    Memory is an essential aspect of language learning. If you don't address this issue then you are doomed to waste hours revisiting material unnecessarily.

  8. After reading and speaking, there is listening. (As I already said, forget about writing. Writing is a special and very advanced skill, even in your own language, that you cannot begin to contemplate until you've read extensively over several years.)

    This is hard. We don't actually hear what people say unless we already know what they are saying.

    WTF!?

    I'm still trying to understand the process, but so far it seems that we replay what we (think we) hear in our ears so that we can understand it in our heads.

    But it happens so fast that you have to train your "ear" to be able to process the sounds instantly. There's no going back (except in a one-to-one conversation where you can ask the speaker to repeat him/herself).

    The way to do this effectively is to read and master the text that you want to be able to understand aurally. And then listen to it over and over again, one sentence at a time, until you can hear - pick out and understand - each word clearly.

    That's why I've created audio-ebooks for each of the "fluency" courses so that you can listen and read simultaneously using a remarkable app called Listening Drill.

    I also recommend listening to original-language movies with subtitles on (in the same language, not in yours). This of course means being able to play the movie slowly enough so that you have time to read the subtitles! It's not easy - and I've devised a way to do this so that you can follow a movie at your own pace.

    When you can see what's being said then you can also hear it!

    In time, you will be able to hear similar patterns of speech without the support of the written text.

    This is a crucial component of the Rapid Method. Many courses do include listening material, but not in the form of "ear training". In the Rapid Method, you are expected to listen to each sentence repeatedly before moving on to the next one... not just listen to as much generic material as possible in the hope that you will eventually become "attuned" to the general sounds of the language. I think Glossika tries to do this, but I didn't find it useful for me - perhaps because it was too unstructured with no integration with the text and no learning path. And although Glossika is available in a "spaced repetition" version (a bit like Pimsleur), it's poorly implemented. One needs to be able to control this process yourself.

    I tried "massive listening" when I first came to Thailand. I watched a movie every day (with English subtitles) for a year. It was a spectacular failure: I learnt nothing. My mistake was to switch on the English subtitles. This meant that I tuned out the spoken dialog and just focused on the meaning. But even when I tried watching movies with no subtitles, I didn't hear - or understand, or learn - anything. In Stephen Krashen's research, he states that you need "comprehensible input" in order to make any progress in learning a language. I.e., you need to be able to understand what you are hearing, otherwise it is a total waste of time.

    What I did find useful, however, was attending the AUA classes in Bangkok (AUA elsewhere in Thailand don't follow the same method for some reason). Two teachers will talk and mime and draw in front of the class and all you need to do is pay attention and listen. You'll get the gist of what they're saying.

    The theory is that your mind will undergo mild stress and tension and will be forced to "stretch" into a state of understanding, exactly how children learn.

    I don't think this is efficient. It's more efficient to choose a level where there is no tension, where you understand mostly everything comfortably, and then just sit back and enjoy the show!