The first language

Everyone has his or her main language; we call it sometimes the first language or the mother tongue. Some people grow up with two languages; one is the language of the society, the streets, the city or the country they live in, and the other of the parents. One of these two languages necessarily dominate the other or preferred to be used, in other words, those who grow up with two languages, whom we might call the multiculturalists, the multi linguistics, the multi-tongues or whatever they might be called, prefer to use one of the two languages, they prefer to use the language which they can control the most, the language which they think easier and more natural to them. This language is their first language and the other is the second. The two languages could not be a first language at the same time. It could be that one is the main at an earlier age and the other could take its place at an advanced age. For example; children under the age of five who live with their parents commonly use their mother language and above the age of five they use the country language. In any case it depends on the people and the community around and the time children spend with each side (the parents and the community). Spending more hours of the day with side one (the parents) makes the child pick up his or her parents language as a first language, and the opposite will happen when the child is spending most of his or her time with side two (the community). At an early age it's easier and faster for a child to change his or her language and to form a native and natural accent with the new language but it becomes a little harder between the ages of ten and fifteen. As for people above fifteen it's much harder to replace the main language and accent; the accent in particular is even harder if not impossible to be changed. It's possible for people over the age of fifteen to change their main language, take control of the new one and make it their first and most natural language; but the accent will remain affected by their old main language for a long time.
This is the way we learn our first language, from life. There is no specific time to sit beside the desk and learn as we usually do when learning anything. To learn a language, all the time is a time of learning; the more we listen, speak, read, write, think and speak in our minds, dream while sleeping and live the days the more we learn and control the language.
Learning any science, away from learning actions and movement skills, is just learning new nouns, verbs, adjectives, and etcetera. It's just learning a language. Learning a language is harder than learning anything else; it needs more time and more efforts. That is why it's hard to learn a new language and control it like the main. To control the new language like the first we need to learn everything we learnt while using our first language.
English is my second language; it will never be like my main Arabic language unless I spend another thirty years using it as I used Arabic before.