What term describes a kind of speech or language that is informal and region-specific?

The term that accurately describes a kind of speech or language that is informal and region-specific is "patois." This word is often used to refer to dialects or forms of speech that arise in specific communities, particularly those that incorporate elements from various languages and may serve as a marker of cultural identity. Patois emphasizes the informal and localized nature of the language, showcasing how it can vary significantly from the standard language of a region.

In contrast, the other terms do not relate to informal dialects. "Ossify" refers to the process of becoming rigid or inflexible, often in a metaphorical context relating to ideas or structures becoming outdated. "Penurious" describes a state of being extremely poor or frugal, which has no relevance to language or speech. "Ostentation" denotes a showy display intended to impress others, often in terms of wealth or status, again unrelated to the concept of informal, localized speech. Thus, "patois" stands out as the only choice that specifically captures the essence of informal regional language variations.