True bilingualism

When we talk about true bilingual, we mean two principal conditions:  the first, the subject speaks two language in the same level.  None of those helps to define bilingualism due no one speaks a language “`perfectly” and linguistic performance cannot be measured and what it is not measured cannot be compared. It is said that even vocabulary could be meaningless. A person cannot go through linguistic experience twice for example, a person who has worked in two different countries like England and France, that doesn’t mean that the individual will know both language perfectly. Equality between two linguistic performances has to be approached in a different ways. The second those both language are her or his mother tongues and it is acquire by immersion. (We explain in the four subtitle of one part). The child acquired her (his) mother tongues in the environment in which she (he) develops at birth. After the child acquired the mother tongues she (he) can have the speech-learning mechanism. (Chistopher Thiery, N.D.)