What is the most critical factor for a language to maintain its long-term vitality and avoid endangerment?

💡 Explanation:

Unbroken intergenerational transmission—the process by which a language is passed naturally from parents to children within the home—is considered the single most critical factor for a language's vitality. The breakdown of this transmission is the primary indicator of language endangerment, as identified by frameworks like UNESCO’s Language Vitality and Endangerment criteria. If children stop acquiring the language as a first language, its long-term survival is immediately threatened, regardless of its total number of older speakers or official status.