Which languages your community still holds —
and which are down to one speaker.
A language does not disappear all at once. It thins. The grandparents speak it, the parents understand it, the grandchildren know six words and a song. By the time anyone notices, the last fluent speaker in the family is eighty.
Language Preservation makes that visible while it can still be acted on. It shows every language present in the network, how many words of it have been recorded, and — crucially — who in the community still speaks it, generation by generation. A language held by one person in the oldest generation and nobody younger is a different situation from one spoken by all three.
This is not the vocabulary library. That is a place to read words. This is a measurement of what is being lost, and how fast.
You cannot preserve what you have not counted. Count it first.
A term, a pronunciation, and an example of real use. A word held without its usage is a dictionary entry; a word held with it is something a grandchild can actually learn from.
Entries can be marked sovereign, which keeps them within the network that holds them. Nothing is published outward, indexed, or made available for training by anyone.
ECO never authors terms in a language it does not belong to. An invented entry in an endangered language is more damaging than a missing one, because revitalisation work may pick it up and carry it forward as fact.