I was talking to a Year 7 class today about language dominance shift -- which is what can happen if someone stops speaking a language for a long time and/or vigorously speaks a new language in a sustained manner. Obviously people can become more fluent in a language w/ continual practice, but they can also become less fluent in a language if they reduce or stop practising it.
Here's an example: Barack Obama vs Kevin Rudd (note: this is NOT a political discussion, I'm purely using two public figures to demonstrate the acquisition and deterioration of language; please do not deviate from this focus)
Barack Obama
As a young boy, Obama moved to Indonesia with his mother and step-father where he lived for several years of his childhood, and attended a local school. As a result, he learnt to speak Bahasa Indonesia. Forty years later, Obama returned to Indonesia, however his Indonesian only appears to be partially conversant. In this short excerpt of Obama's 2011 speech at the University of Indonesia, we can see that Obama is predominantly speaking in English, with a few Indonesian sentences and words here and there. Presumably Obama may not have spoken much Indonesian (if at all) since moving out of Indonesia, thus the deterioration of this proficiency in that language may likely be a result of those decades of disuse. Compare this with...
Kevin Rudd
Learnt to speak Mandarin Chinese as a university student, so he was already a young adult -- and learning a language in adulthood is considerably harder than in childhood. Then of course, Rudd went on to live and work in China. It is widely known that Rudd is perfectly fluent in Chinese.
