Anyone who has ever needed to communicate with a non-native speaker, or has simply heard one speak, must have at some point wondered at the style of speaking they were hearing.  What accounts for those peculiarities?  Why is it that they rarely ever learn what they are taught?  Why do they seem to make the same mistakes over and over even though they know what is correct and are trying their best?  In order to understand why learners use the target language the way they do, one must understand the concept of interlanguage and the processes by which interlanguages are formed.

"Interlanguage" is a term that refers to the integrated system of knowledge about the target language that the language learners are constructing in their minds. It is very similar to the concept of competence in that it is the learner’s internalized and systematic knowledge or ability to use the target language to communicate. In fact, it could be considered a kind of competence. It differs from the general concept of competence however in the fact that the term "interlanguage" implies that the internal language system is still unfinished. It is a work in progress.  Whereas the term competence could refer to a native speaker, the term interlanguage is only used to describe a learner's incomplete knowledge in  a second language. The learner is trying to construct a system of second language competence but still has not acquired all the target language rules. The term interlanguage also implies that the learner’s first language is playing a role in this process. Although the interlanguage is a separate system from the first language competence, it still shares certain characteristics of the first language. Likewise, the interlanguage, is also not exactly the same system as the second language but shares some of its characteristics too. In that sense, it is seen as being somewhere between the two languages - an interim language system, slowing progressing away from the first language system and moving towards being a closer approximation of the second language system. This forward movement is made as the learners discover the rules of target language through a process of creative construction.

During the process of creative construction, learners actively seek information about the target language from many sources and then try to apply those notions about the target language to their interlanguage. Information about the target language may come from many sources. These sources include, assumptions based on the learners’ first languages, assumptions or generalizations based on what they already know about the target language, information they receive about the target language from textbooks, dictionaries, and teachers, or even the learners’ own attempts to communicate. For beginning EFL learners, the most important source may be textbooks and teachers, but for other learners information may be induced from actual target language input and real experiences with the target language. In either case, the new information will not immediately affect the interlanguage. In other words, learners cannot simply acquire every rule that they have been taught in a class or seen in books. Likewise, they do not simply acquire every form they hear in their input. New forms enter this integrated system in stages. First, learners must notice some form that they would like to learn and that seems to be within their reach. Then they form some sort of hypothesis about that form. For example, a learner might hear the word "because" being used by a native speaker to state some reason or explanation. For example, the speaker may have said "I don’t eat ice cream because I am on a diet." The learner who hears this may then infer that the word "because" may be used for that purpose, but still may not know exactly how to use it. She may then attempt to use it in a manner similar to how it is used in her first language. In this case she might assume that it is used as a subordinator in between two clauses, just as it is used in her first language. She may then test her ideas when speaking. For example, she might say "I wear jacket, because today weather is cold." If communication is successful and she gets no negative feedback, then she will continue using the form that way. In this manner, forms are incorporated piece by piece into the larger integrated system of the interlanguage.  Although the explicit teaching of form in a language classroom might be a source of knowledge for language learners, ultimately, it is the learners themselves and their current interlanguage state which determines what new forms will be taken in.  A teacher or a syllabus cannot determine this process.  In conclusion, learners do not always learn what they are taught and even tend to learn things they are not being taught.

Yet another process that is very involved with interlanguage construction is internalization.  Internalization refers to the process by which something gradually gets more deeply inside the learner's interlanguage.  Most language researchers believe that this process generally only happens during practice which is authentic, communicative, and meaningful, such as the real communication that one might experience in a country that speaks the target language.  During communication, the meaningful and authentic practice pushes target language forms more deeply inside the interlanguage making them more automatic.  Those internalized, and therefore automatized, forms come out when the speaker needs them without the speaker making much effort or having to concentrate any energy on the form.  On the other hand, some forms that have been learned recently and haven't been used much can be referred to as "known" but not fully internalized.  Those forms are to some degree inside the interlanguage but are not yet really inside.  They will not come out automatically when the learner is speaking, and therefore, take a degree of effort to use.  This situation can be illustrated by the many forms that learners have studied in language classes but never actually used in real-life situations.  Most learners learn forms such as the past tense "ed" morpheme in their first year of English study but may not be able to control that form when speaking for many years.  While speaking they will naturally have a tendency to focus their mental energies on the meaning of what they are trying to produce and the other new forms or new vocabulary that seem more important for saying what they need to say.  Eventually, after more vital forms, such as the basic word order, get internalized, the learner will be able to concentrate more on using the past tense form correctly, and only then, gradually internalize it. For this reason, all the forms do not get internalized simultaneously, nor do they get internalized in the order they were taught, but moreover, they get internalized when the learners themselves are ready.  A developmental order for the internalization of forms necessarily follows as learners communication drives them to focus on the most meaningful, necessary, frequent, and noticeable forms first.  Thus, forms that aren't completely necessary for communication, such as articles and the third person singular "s" morpheme, are generally internalized very slowly.  In conclusion, learners often cannot consistently use a form even though they know it well and have been studying it for years.  Sometimes these troublesome forms are even semantically and mechanically simple, yet won't get internalized unless learners struggle with them for years.

When listening to a language learner struggle to produce a second language, we must understand this process so we can be more sympathetic of their struggle.  If we do not understand this process and the struggle language learners are engaged in, then we might be likely to believe that those learners are either lazy or stupid because they cannot or do not consistently produce even the "simplest" of grammar forms accurately and seem unable to apply what they are taught.  Teachers who misunderstand this process and mistakenly believe that they are in control will get angry when confronted with their students' lack of progress or inability to use what they have learned.  Teachers who do understand this process will be more sympathetic and will provide their students' with learner-centered opportunities to discover the rules of the target language and internalize it through communicative activities.  In summary, understanding this process is key to being a "good" language teacher, or at least one who is sympathetic and effective.