Obviously, language is a core differentiator – and the core binder. Instantly one can tell if someone belongs to the group.
There are always rich differences, not just in the vocabulary, but in the way life is viewed and interpreted. Adages, metaphors and humor all reflect the culture as well, informed by distinctly different points of view.
Even within a language it is not one-size-fits-all. Regional differences make it possible to identify which part of the country someone is from. These differences can be the subject of teasing. As a Mainah myself, I do pahk my cah.
Cultures abutting one another in a region or even a neighborhood, often build language bridges. Conversations can be peppered with newly developed common words.
How we speak tells our story.