What is culture?
What defines something as cultural?
When does a sub-culture become its own culture?
What defines culture?
Something is cultural when it is a tradition, aspect or custom at least somewhat unique to that culture
A sub-culture is a culture within a culture, which retains most or all of its parent culture’s aspects but has its own distinct flavor
Can religion and language be considered part of a culture?
With religion, Yes, but only if it is a core component of the culture
Language is more tied to ethnicity, which encompasses a broad field INCLUDING but not limited to language, culture, heritage, etc.
Google has a very accurate definition I’d say. But yeh language is the ultimate manifestation of a culture @Ka1serTheRoll . It’s why when studying it you need to listen to and talk to a native speaker, if you don’t you will unknowingly inject new words and even grammar into the language, this has happened many times with English. Irish English for example borrowing grammar from Irish itself, I remember being chastised online for terrible English when in reality it’s my dialect they don’t get. But this is even more pronounced in Singapore and China where subtle cultural elements and rules have slipped into their rapidly developing English dialects