Individuals learning a second language use the same innate processes that are used to acquire their first language from the first days of exposure to the new language in spite of their age. They reach similar developmental stages to those in first language acquisition, making some of the same types of errors in grammatical markers that young children make, picking up chunks of language without knowing precisely what each word means, and relying on sources of input humans who speak that language-to provide modified speech that they can at least partially comprehend (Collier, 1998). Second language learners are usually observed developing a new language system that incorporates elements from the native language and elements from English they recently learned.
Inter-language actually helps second language learners test hypotheses about how language works and develop their own set of rules for using language.