Would a language be forgotten after prolong disuse?

Language development involves two processes in the brain, (1) an operating system of voice recognition and (2)a data base of vocabularies and contents.

The voice recognition system is developed during a critical period in the first 9 months after birth, with the automatic wiring of language neurons. As an operating system, like the CPU, it is kept for life.

The data base of vocabularies and contents is like a hard disc. You can input data any time. But you can easily lose it after prolong disuse.

How do we know that the voice recognition system is kept for life?

We can only recognize sounds that are found in our voice recognition system. When the brain receives an alien sound not found in the system, it will be directed to the nearest sound in the system. Japanese cannot distinguish between L and R. Indians will say "dan giu" instead of "thank you".

For people who have completely forgotten a particular language, they can pick it up much faster than people who have never been exposed to that language. They can imitate and pronounce the words like a native speaker. This ability is not found in people who have never been exposed to the language.

Multi-lingual speakers are far more gifted in learning new languages than monolingual speakers. Multi-lingual speakers have a voice recognition system far more powerful than that of a monolingual speaker. When you can recognize a sound, you can say it. When you cannot recognize a sound, you can't.

So, don't worry if you have forgotten a language because of prolong disuse. Spend a little time on it in building up the necessary vocabulary, the language will come back quickly.

http://www.psychologytoday.com/blog/life-bilingual/201103/language-forgetting