Most of the non-native languages have, to different degrees, evolved differently from the mother country, but are usually still mutually intelligible.
On the other hand, adults are said to 'learn' a non-native language.
This is due to infants experiencing their native language often, while not getting much experience with non-native languages.
All undergraduate students at Soka University of America must study a non-native language.
Pronunciation is the most difficult part of a non-native language to learn.
Most individuals who speak a non-native language fluently speak it with an accent of their native tongue.
There are also rare instances of individuals who are able to pass for native speakers even if they learned their non-native language in early adulthood.
Most researchers agree that for adults, acquiring a native-like accent in a non-native language is near impossible.
Michael Sharwood Smith (born 1942) is a researcher into the acquisition of non-native languages.
We also insist on the importance of learning two non-native languages from an early age, including those of neighbouring countries.