Generally, language death occurs as the result of a people being in physical danger or because of cultural assimilation; but as David Crystal suggests, it is not always that simple, “It is not usually possible to write a single cause on the death certificate for a language” (Language Death, 2000).  Specific reasons for language death include the following:

Demographics (e.g., urbanization - economic factors luring rural works to urban areas);

Language Use (e.g., after the Babylonian Captivity, the Hebrew language was virtually dead; however, within the last century, Israel's implementation of aggressive language planning and policy and the use of Ulpanim, intensive Hebrew language immersion schools, have revived the Hebrew language in Palestine);

Language Cultivation, Development, Literacy;

Status and Recognition (usually indigenous languages just aren't invited into a country's education system, the press, or religious life; but Paraguay is an exception.   There, the Guarani language population enjoys equal status with Spanish);

Language Attitudes (individual, regional, national - e.g., speakers in that language have a booming economy or international or regional prestige and power; According to linguist, K. David Harrison of the Living Tongues Institute, “Children are little barometers of social prestige.  They understand implicitly that if they live in an environment where two languages are spoken, one of them is less valued than the other, and they will speak the more valued language.”);

Amount and Quality of Documentation (dictionaries, the Bible, other literature, etc.);

and the Number of speakers (but the number of speakers is not necessarily deterministic in the life of a language).

Since merely saying that a language is "endangered" can be ambiguous, it is needful to define levels of endangerment.  Although various linguists may have their own definitions, which differ to some extent, the following will provide an idea of how a language ranks among various levels of vitality.

Potentially endangered – lack of prestige in the home country, economic deprivation, language not being passed on in the education system

It's important for a missionary to understand sociolinguistc factors involving languages so they do not inadvertently contribute to the demise of the language.  A missionary who learns a people's language honors that people by his efforts.   But sometimes, missionaries are tempted to learn majority languages in order to operate as foreigners in their host culture.  Some missionaries who do this resist the further work of learning the language of the target people because some of them also speak the majority language.  But stopping short of the target people's mother tongue is unprofitable for the lost.  And missionaries who learn majority languages prior to learning their target language may unknowingly be telling their host culture which language they believe to be the more important language (i.e., the one they learned first).  And not surprisingly, giving a minority language group a Bible is actually a huge step toward language revitalization.

The concern or lack of concern about language death is a matter of perspective.  A person ignorant of God and apathetic to God's message will merely value cultural and historical losses when languages die.  They care about language death because of cultural and historical loss.  But a person who knows God and is motivated to give His message to all people will see language death as the most significant communication failure imaginable.  How would you like have to learn a second language in order to partly understand God's message to you?  This is not God's will.  His message is for all people, tribes, tongues, and languages.  Let's give them the Message in a language they can understand - theirs!

Statistic:
The median size language in the world is 6,000 speakers.  This means that half of the world's languages are spoken by 6,000 or more people; and that the other half are spoken by 6,000 or less people.

David Parker