after having used a plethora of language learning methods and materials, I maintain that the ideal ones for me are language books designed to be used in class, either at a language institute or in school.
I definitely cannot recommend any of the "Teach Yourself" solutions I've seen and used so far, and they were plenty: Assimil, Pons, Langenscheidt, Hueber, Lextra, Colloquial..., Teach Yourself..., Pimsleur, among some others.
The fundamental problem with any Teach Yourself material is space: It is definitely not possible to summarize a whole language in a book, let alone in a 100-page book full of illustrations. Too many things must be neglected in order to "help the learner reach level B2". And by things I mean grammar structures, pragmatic chunks, intonation patterns, cultural aspects and useful vocabulary that are just not there, which ends up making the learner look for third-party resources anyway.
The pace the learner has to keep while using a Teach Yourself is just too quick for any meaningful learning process to occur, while the vocabulary inventory is in many cases strange, if not useless: My Bulgarian Teach Yourself taught me how to say "rape", "kidnapping" and "murder" in lesson 5.
When I start learning a language, my ultimate goal is to become functional in the language in all four basic abilities: reading, writing, listening and speaking. Most Teach Yourself materials focus just on the oral abilities while completely neglecting the written ones (at least writing, if not both).
In order to become functional in the language, I must be able to use it for any purpose I might need it, such as (from easiest to hardest) communicating with friends, traveling, researching and working. In my specific case, I might need to be able to write academic papers in the language, which requires quite a fair amount of fluency. Up until now I have learnt (or am still learning) 14 languages. I know I may not reach my desired C1 level in all of them, but that remains my ultimate objective, no matter how far I may be able to advance. I've realized very early in life that setting clear goals for myself tremendously increases my chances of getting there.
Having said that, I would like you to do a self-brainstorming exercise right now and ask yourself why you are learning the languages you have chosen to learn. What are your general objectives and specific goals? What do you want to use your languages for?
Let's suppose for one minute, for the sake of argument, that your objectives are similar to mine. Now, look at your Teach Yourself - Can you sincerely picture a scenario in which you achieve such goals just by using that? If your answer was no, we've come to the same conclusion.
Having realized that myself, I started looking for "more serious" materials, books that would really take me further than those linguistic summaries.
I've been using course books for a while now, and I'm probably not going back. They are much more in-depth, vocabulary-rich resources. The pace they keep is slower, just as a language learning process should be. Such books have multiple volumes, usually one for each level. They are much more thought-out works than Teach Yourself books, and here's why: Course books are written by (Applied) Linguists, professionals who know exactly what they are doing, even when they do it wrong.
For a course book to be adopted by a language institute, its method must fit the teachers'/course coordinators' beliefs in language teaching/learning approaches and methods. The books are therefore inspected and analyzed before being put to use. For a course book to be adopted by a nation's Ministry of Education the process is much longer and more thorough. Designing a course book is an unbelievably complex endeavor that takes (in many cases) years to accomplish.
On the other hand, Teach Yourself authors sprout in droves and manage to publish their works, in many cases without anyone's proofreading them (I can't stand the typos in my Teach Yourself Persian anymore). But most aggravatingly, many of such authors are simply not qualified for the job. Just yesterday someone sent me the link to "an awesome Teach Yourself Greek" for Brazilian Portuguese speakers. I then accessed the website and clicked on the "About the Authors" tab: "Mr. John Doe is a Civil Engineer who..." (...) Mrs. Jane Doe is an Electronics Engineer who..." and I quit reading right there.
I'm not saying people without academic credentials simply cannot produce anything of value, it is just extremely hard to find such a thing. Language teaching is not an art which someone may master without ever receiving formal instruction on it - it is a science, a very complex human science whose basis is an inventory of millions of pages of linguistic theories, peer-reviewed articles, Doctoral Theses, action-research, focus group analyses and triangulations that have up until now been grouped into 4 main language teaching approaches and dozens of corresponding language teaching methods, each of which has been tried and tested by hundreds of teachers and thousands of learners in every continent.
There is certainly something there that you simply cannot find in many Teach Yourself books. Again, mutatis mutandis, there are some Teach Yourself books that are scientifically designed. They are, however and unfortunately, few.
Nonetheless, when using a course book, one must be aware of a specific set of strategies in order to get the work done by himself. As a general rule of thumb, the more structuralist the book is, the better it works with me. Structural methods do not rely much on communication among learners, especially at the beginning. If you use a more communicative-based method, the conversation exercises should be done entirely by yourself, by means of self-talk or inner-talk, which means you will be practicing the language twice as much as if you were actually in a learning group. The main problem with that is lack of feedback - it is very hard to learn a language without an instructor because you really don't know whether you are doing it right until you receive such confirmation. For that, the only thing I can recommend is that you find yourself a language partner (preferably a native speaker, preferably a teacher) to correct you whenever needed.
Course books always have accompanying exercise books, which, though monotonous, are the key to language learning. Whatever you do, remember this: Our memory works by means of the establishment of neuron pathways. These pathways are created by repetition, confirmation and association. Have I mentioned repetition?
Sometimes the exercise books don't include the key to the exercises. In this case, you have to look for the Instructor/Teacher's Edition of the book and you'll find all the answers there. As I have access to a very comprehensive library in my city, what I do is to borrow the Teacher's Book and copy the answers. The most practical way I've found to do that is to use an app called "CamScan" on my phone and take pictures of each page, which I can then convert to text or save as a PDF file.
There's also no need to mention that every course book nowadays comes with CDs, DVDs or MP3 files with dialogue recordings. These are essential for autodidacts because without a teacher (or knowledge of the IPA) learners have no basis to build their pronunciation upon.
What follows below is a very short review of the course books I am using at the moment or have used in the past. If you would like to get more info on any of them, don't hesitate to ask. This list will be particularly useful to those who already know German, as many of the books on my list are published in Germany and in German.
English - New Interchange (all levels) in English
This book by Jack C. Richards is widely used in language schools in Brazil. It follows the communicative approach and is a very comprehensive, well-designed book.
German - Themen (all levels) in German
I've finished my German course at Goethe Institut more than 10 years ago and Themen was one of the few available books at the time. It's quite structural, but keeps a nice and slow pace and the vocabulary inventory is very rational. By the time I got to C1 level, a new edition was published, Themen Neu. As far as I know, it's not been used much these days and it may be hard to find it. I can also recommend Tangram, Schritte and Moment Mal!
Dutch - Taal vitaal (A1-A2), Taal totaal (B1-B2) in German and Dutch
Unfortunately, there aren't many materials for Dutch published in Germany and this book is certainly not the best I've ever used, but it does its job. It follows the Communicative Method and, in order to use the book for autodidactic learning, you'll have to use a lot of the self-talk strategies I discussed above.
Swedish - Rivstart A1+A2 and Rivstart B1+B2 in Swedish
This is one of the best I've used so far. Rivstart is very comprehensive, yet very simple to follow. It is not meant to be used by autodidacts, but it may (almost) perfectly be used this way.
Spanish - Hacia el español (A1-B1) in Portuguese and Spanish
This one is aimed at speakers of Brazilian Portuguese, so you might find it a bit difficult to follow if you have any other language as your native language, due to the similarity between Portuguese and Spanish. I've mainly used open-learning resources to practice Spanish, so I can't really recommend any course books.
Italian - In Italiano (A1-B2) in Italian
A very, very structural book, with a massive amount of exercises for each lesson. It works if you are the kind of person who tolerates reading, saying and writing the same thing over and over.
Brazilian Portuguese - Falar... Ler... Escrever... Português (A1-B1) in Portuguese
This Brazilian Portuguese book is used in many universities and language schools in Europe. It's labeled a structural-communicative method, but it's mainly structural, as evidenced by its many exercises on verb conjugations. It may be used without many problems by autodidacts.
French - Grammaire Progressive du Français (all levels) in French
Not a course book per se, more like a grammar with exercises, but it's used in language schools nonetheless. I like the way this book is structured, grouping grammar topics and related vocabulary. This is ideal for self-learners, but it hardly allows for any speaking practice (even by means of self-talk).
Unfortunately I can't recommend any course book for Romanian because I've yet to find a good one. If you are a German speaker, please stay away from both the Lehrbuch der rumänischen Sprache and Rumänisch für Sie. They are, simply put, intolerably bad. What I use is a grammar by Pons called Pons Power-Sprachtraining Rumänisch. It's quite good, contains grammar as well as vocabulary sections and exercises and comes with a CD.
Greek - Ελληνικά Τώρα 1+1, Ελληνικά Τώρα 2+2 (A1-B2) in Greek
It's the most structural book from this list. This course book offers tons of exercises, a grammar section in English at the end, vocabulary lists, lists of verbs and very nice dialogues that portray the story of a group a characters from the beginning to the end of the book (SPOILER ALERT: the protagonists marry at the end!)
Same thing as Romanian. The book I have used is a horrible Teach Yourself by Pons. I currently have weekly online lessons with a native Bulgarian and she designs her own material.
Persian - Persisch für Anfänger (A1-A2), Persisch für Fortgeschrittene (B1-B2) in German and Persian
The lack of materials for Persian made me buy this book and unfortunately I can't recommend it with a clear conscience. There are two main problems with this book: 1. It teaches you formal Persian, while my main interest is to learn the colloquial, everyday language and 2. Its vocabulary inventory is quite ridiculous. Lesson 6 includes words like "donkey", "to flow" and "garlic", not in their corresponding semantic fields, but as single words! One thing good course book designers have long understood is that if you are going to teach a word, teach the whole semantic field and have your learners memorize everything by association. It works, trust me!
Hindi - Hindi Bolo 1 (A1-A2), Hindi Bolo 2 (B1-B2) in German and Hindi
This is a very well-written book, with tons of dialogues and exercises, it keeps a nice development rhythm and may be easily used by self-learners.
Hebrew - עברית מן ההתחלה חלק א (A1-A2) and עברית מן ההתחלה חלק ב (B1-B2) in English and Hebrew
This is a nice book, specially the first volume. It contains a lot of texts and comprehension exercises, as well as very well-written grammar explanations. The main problem with this book is that it is meant to be used at the Ulpanim in Israel for those who make Aliyah. For that reason, it contains too many religious topics in its texts. As I am not directly interested in the Jewish religion, I can't help finding the texts that are exclusively dedicated to introducing religious vocabulary extremely boring and quite useless to me. But other than that it is a great book.
There are many constraints in using course books as self-learning materials, some of which I have discussed above, but the fact that they are much more comprehensive than Teach Yourself books compensate for many of their flaws.
One main problem, though, is the irritating lack of materials for advanced learners (C1+). The gap between B2 and C1 is in my opinion the most important achievement for a language learner. It represents the difference between being able to converse in the language with native speakers for two hours about amenities and being able to work in the language, formulate complex arguments and sound "smart", even in demanding conversational environments. Unfortunately, the only way to overcame this gap is by using the language as much as you can, getting feedback from native speakers and ideally working with a language instructor, because there are simply not enough written materials for advanced learners in many of the world languages, even in popular European languages like Italian and Spanish, let alone in languages like Greek, Swedish, Persian and Bulgarian.
I should also mention that course books are not the only things you need to learn a language. For every language I learn, I look for the following materials (usually in this order):
1. Course books
2. Bilingual dictionary (English-X for languages like Persian and Hebrew, German-X for Germanic languages, Spanish-X or English-X for Romance languages)
3. Monolingual dictionary (generally at a more advanced level)
4. Verb dictionaries with conjugations (not for the Germanic languages)
5. Vocabulary lists and Semantic-field dictionaries
Other than that, as soon as you reach a certain level, you'll start to need more comprehensive, original sources, the so-called open-learning sources: newspapers, magazines, TV shows, songs and anything written or spoken in the language you're learning. Fortunately, with the Internet, such content has been popularized as much as it can be, and the ubiquity of free open-learning sources is perhaps the biggest difference between a 21st-century learner and a 20th-century learner.
Lastly, always keep in mind that your choice of materials will depend exclusively on the goals you want to reach. Don't fool yourself, though. Properly learning a human language will certainly require much more than an illustrated 100-page booklet.
Thanks for taking the time to read this.