First of all, I need to clarify that I want to say "language exchange does not work for everyone", which means that it works for some people but at the same time does not work for others. Explanations are given below point by point:
1. Language exchange is for practising, not learning.
Unless you are a very good looking person and your partner wants to learn more than your language, usually your language exchange partner would not have the patience to teach you the basic of the basic that can be self-studied, e.g. ABC of English, Hiragana of Japanese, bpmf of Mandarin Chinese, etc. Normally, when you take part in a language exchange, you are expected to have some knowledge of your target language already. Otherwise, you will either end up being unable to communicate efficiently with your partners or speak more English than the language you're trying to learn.
So if you are a total beginner, pick up the textbook before engaging in a language exchange. I mean, are you expecting to use Romaji in your Japanese language exchange? Give me a break.
2. If your mother language is a small language like Icelandic, forget about it.
My mother language is Cantonese, which is spoken by 26 million people around the world (according to Wikipedia). It is by definition a big language. But I can tell you that if I want to find a language exchange partner to practise my English, the chance for me to get one is pretty low. It's because the supply of English speaking people who want to learn Cantonese is way smaller than that of Cantonese speaking people who want to learn English. I have no evidence to support me but I guess the ratio is 1:10000. And for a 30-year-old not good looking man like me, the chance is even lower because no one wants to learn more than my language.
So if your mother language is a small language that is spoken by less than 1 million people, and you are trying to learn a big language such as French or German, you will face keen competition in getting a partner.
I know you can speak and teach English even though it is not your mother language. I can too. But my friend, ask yourself if you are to learn French, will you choose a native French speaker or a fluent advanced learner from China as your partner? If people are given a choice, no one wants to do language exchange with non-native speakers. This is the cruel truth you need to remember.
3. Even if you are a native speaker, you will have troubles if you do not speak the textbook accents.
This goes for English speakers especially. English is either taught in BBC or CNN accents around the world. So learners expect you to speak like the news announcers on TV. If your accent is considered "incorrect" such as the Australian "to die" (today), your market will diminish and your "market share" will be taken by your American competitors.
4. You will over-estimate yourself.
I like speaking with monolingual Japanese people, because their ears are more critical. Whenever I say something grammatically funny or an accent too strange, they will honestly tell me (sometimes from their facial expressions) that they don't understand. So when my Japanese sucks, I immediately know it sucks and then try my best to correct it. I learn much faster this way.
But when it comes to bilingual Japanese people, their ears are polluted by English and thus more tolerating. They can magically understand me even when my accent or sentence structure sucks. And then I will lie to myself that my Japanese is okay. At the end of the day, I become a fluent Japanish speaker. Isn't it a waste of my time? Okay, I admit that I don't like speaking with bilingual Japanese people because most of them in Hong Kong here are men in their 40s. (laugh)
In a language exchange, usually your partner is multilingual, especially when neither your language nor your target language is English. The problem is that your partner can understand you even if your grammar sucks. He/ she will simply ignore the problems to keep the conversation going on. And ask yourself, if you spot two mistakes in every sentence your partner says, will you have the courage and patience to correct him/her one by one? To be honest, what you want is learning his/her language, who give a xxxx if he/she can learn your language at the same time, right? Your partner, unfortunately, will have the same mindset. So once again, monolingual people are the most honest in this regard.
5. You spend two hours doing something that can be done in one hour.
In a fair language exchange, you should spend half of the time teaching your language and your partner should do the same by spending half of the time teaching your target language. If this balance is not kept, the whole thing will become teaching and learning, not exchanging.
So it is clear that language exchange is not a free game. You need to pay one hour of your life for one hour of your partner's life. If you have a day job and two kids, do you have the extra one hour to pay? Wouldn't it be more efficient if you speak to monolingual speakers who do not expect you to teach them your language?
6. Most important, not every native speaker can teach.
Native speakers by default have not "learned" their mother language. So they cannot understand why you cannot pronounce certain words correctly. If you don't believe it, you can try to explain to a Japanese the difference between "correct" and "collect". I bet you will give up in order to keep the conversation going on.
A good language teacher should not only have good knowledge about the language taught, but also about the student's mother language. For example, if you don't know that Cantonese does not have English "b", "g" and "d", you won't spend extra time to teach your Cantonese speaking students the correct pronunciation of "boy", "girl" and "dog". Or when you teach an English speaking student Japanese, if you don't know that English sentence must begin with a subject, you won't tell your student that subjects are always skipped in Japanese. And your student will end up beginning every Japanese sentence with "watashi" or "anata".
Self-study or take courses to make it up to intermediate level so that you can communicate with native speakers of your target language. Then talk to native speakers who do not expect you to teach them your language in return. When they laugh at your accent, don't be angry. They are the best teachers you can ever get. Self-respect is nothing when it comes to learning a foreign language. I mean everyone will laugh at your accent in their heart until you correct it to a not funny level. Isn’t it true?