Orthography
A writing system for a language, including which sounds get written and how.
UNESCO counts written materials among its vitality factors, and pairs the claim with an important qualification: “There are language communities that maintain strong oral traditions, and some do not wish their language to be written. In other communities, literacy in their language is a source of pride.”
Both halves matter. Writing is not a neutral good imposed on every language, and a community that declines it is not failing a test. Where it is wanted, UNESCO notes what is actually needed — “books and materials on all topics for various ages and language abilities” — which is a far larger undertaking than an alphabet.
An orthography is also a set of decisions, not a discovery: which distinctions to mark, whose pronunciation to treat as standard, which script to use. Revived languages often carry more than one, and the disagreements between them are usually about authority rather than sound.