Your culture could be a la carte: pick a background, pick a lifestyle, pick a community, pick a religion, etc. and all of these go into your "culture." It could be a generic set of tables that cover a wide range of aspects that together define your character's "culture."
Actually, that is what I have been saying. It is alacarte.
The "culture" is made out of the possible background choices.
Change the backgrounds and the culture becomes different.
None of this would require a specific setting. Just some lists to roll on or select from to pick 3-5 elements that make up your culture. I think I like that idea a lot.
The choice of background IS the "culture".
For example, if I pick a Nomadic background. Then the character comes from a nomadic background.
Somewhere in the SETTING a nomadic culture must now exist.
Either the DM included the background because there is one or more nomadic cultures that are prominent in the setting. Or the player is asking the DM for this background, and the DM is willing to find a place in the setting where a nomadic culture can make some sense.
Either way, there is a one-to-one correspondence between background and culture.
Besides background, what else is necessary to reflect a culture? The background can supply a language, and work like History to make Lore checks that pertain to that culture. Nothing else is needed, mechanically, beyond a background.
Meanwhile, a DM might want to point to an area in a setting map to give the player a sense of where the culture is currently flourishing.
Suppose the DM wants a magi-tech Mountain Dwarf culture. The DM can create say 5 backgrounds with magi-tech themes. Think about how a dwarf in that culture would use this technology. Say, there is a Dwarven magi-tech brewery, that uses magic and rituals to produce high quantities of high quality ale. There might be a ritual that allows a character to convert underground fungi into excellent ale. Perhaps the ale is nutritious and serves as a hearty meal (for those with high alcohol tolerance). Perhaps there are even medicinal properties, like removing 1 level of exhaustion extra per long rest, or longevity. Perhaps there is only one particular mountain where the dwarven community is known for their magi-tech. In any case, creating five backgrounds that highlight the main tropes of that community culture, brings the culture to life. The backgrounds help the players identify with the gameworld culture in a fun way.
Meanwhile the "dwarven magi-tech brewer" gains access to the language of that mountain, perhaps a peculiar dialect. Any skill checks about that mountain culture and other cultures that have connections with it (mainly from market contacts), are proficient because of the background.
Does every dwarf speak the same language? Probably not. Humans dont. So the actual language depends on the setting, but the background grants it, whatever it is.
