There is a standard (more formal) Spanish where we all understand each other.
Colloquialisms mark the big differences, but that's the same in any language. Sometimes context helps, sometimes one has to ask what the other person means, but we have a saying: "hablando se entiende la gente" (people understand each other by talking), so any variation you learn, you will be able to communicate with others as long as they want to communicate with you as well.