From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Language_attrition

Language attrition is the process of losing a native or first language. This process is generally caused by both isolation from speakers of the first language ("L1") and the acquisition and use of a second language ("L2"), which interferes with the correct production and comprehension of the first. Such interference from a second language is probably experienced to some extent by all bilinguals, but is most evident among speakers for whom a language other than their first has started to play an important, if not dominant, role in everyday life; these speakers are more likely to experience language attrition. It is common among immigrants that travel to countries where languages foreign to them are used.

There are several factors which affect the process. Frequent exposure and use of a particular language is often assumed adequate to maintain the native language system intact. However, research has often failed to confirm this prediction. A positive attitude towards the potentially attriting language or its speech community and motivation to retain the language are other factors which may reduce attrition. These factors are too difficult to confirm by research. However, a person's age can well predict the likelihood of attrition; children are demonstrably more likely to lose their first language than adults.

These factors are similar to those that affect second-language acquisition and the two processes are sometimes compared. However, the overall impact of these factors is far less than that for second language acquisition.

Language attrition results in a decrease of language proficiency. The current consensus is that it manifests itself first and most noticeably in speakers' vocabulary (in their lexical access and their mental lexicon), while grammatical and especially phonological representations appear more stable among speakers who emigrated after puberty.

Study