We cannot speak if we don’t know how to speak the language and we cannot teach if we don’t know what to teach. Does anyone who can speak the language, can teach the language?
Yes, but it depends to the expertise of the speaker because there are some native speakers who can speak the language ever since they grow up. They use to speak the language in their everyday -life communication with other people in their society. For instance, they can teach some words unless they already know how to translate it and give meaning or simply describe the specific words but not really considering the proper way of learning. One of the examples of this is, if you are going to teach a 3 –year old child the different kinds of animals’ dog, bird and fish. You must teach the differences of the animals by simply putting it into action or by showing some pictures of it or by describing it using some words in such language. And that is what we called the informal teaching in the target language but learning is limited.
But once the speaker done into formal learning in such language then, he/she must teach to the highest level of learning in such language because there is learning that requires the proper way and execution. For example, in our secondary language which is English. The expert and fluent speaker who’s done in his/her mastery and training in an exclusive school has an ability to teach the language efficiently and deliberate learning effectively. So, the learner learns as well professionally.