What are criteria used by UNESCO to put a language into four levels of language endangerment? Discuss while enumerating two examples of Indian languages placed in each of these levels.

An endangered language is one that is likely to become extinct in the near future. As per UNESCO, any language spoken by less than 10,000 persons is considered “potentially endangered”. Not every potentially endangered language necessarily faces the threat of immediate extinction. However, that number indicates a threshold.
UNESCO has categorized languages on basis of endangerment as follows:-Vulnerable, Definitely Endangered, Severely Endangered and Critically Endangered

• Vulnerable: Most children speak the language, but it may be restricted to certain domains (e.g., home).
• Definitely endangered: Children no longer learn the language as mother tongue in the home. 
• Severely endangered: Language is spoken by grandparents and older generations; while the parent generation may understand it, they do not speak it to children or among themselves.
• Critically endangered: The youngest speakers are grandparents and older, and they speak the language partially and infrequently.

Examples for Vulnerable languages in India are: Karbi language of Assam and Adi language in Arunachal Pradesh. Examples for Definitely endangered languages in India are Bawm language of north east and Jad language of U.P. Examples of severely endangered languages in India include Remo language of Orissa, Atong language of Meghalaya. Examples for Critically endangered languages in India are Manda language in Odisha and Handuri in Himachal Pradesh.