From Wikipedia

Himalayas -  Science Of The Mind

In linguistics, language death also language extinction or linguistic extinction, and rarely linguicide or glottophagy
is a process that affects speech communities where the level of linguistic competence that speakers possess of a given language variety is decreased, eventually resulting in no native and/or fluent speakers of the variety. Language death may affect any language idiom, including dialects and languages.

Language death should not be confused with language attrition (also called language loss) which describes the loss of proficiency in a language at the individual level.