Interlanguage is the concept denoting the language between our native and learning language, L2. I consider that the main reason of the emergence of the interlanguage is the lack of sufficient knowledge on our second language. When we are speaking, we try to express our opinion with the words we know in our mother tongue. We apply the words, word phrases, rules, principles of our 1st language to the second one in order to show our understanding. Every individual learner has particular similarities and differences in learning language. When it comes to regularities, learning grammar can be a good example, with the reason that the way of acquisition is the same in every learner, as they learn the rules and work on some exercises for comprehension. Learning all four language skills or vocabulary varies from person to person.