Sign Language itself has had plenty of dialects, more so than just differing between countries, regions or counties, it often varies within cities. For instance I could sign the same sentence to a person in the east and another in the west of Norwich and it’s not unlikely that one of them would tell me that I used an alien sign to them.
This however would likely not affect our conversing much at all, as it is a form of visual communication that in its most pure and contemporary form does not adhere to the structure of spoken and written word (apart from for spelling names), instead functioning in a pictorial manner that passes information as efficiently and effectively as possible.
A drawback of having Sign Language as a primary language means that there are many people in the deaf community that do not have strong reading and writing skills simply because English isn’t their first language. This means that when the vast majority of mainstream film and entertainment is so dialogue-dependent, even with subtitles, a lot of people are getting left out.
To say that dialogue is a key part of modern day storytelling seems all too obvious to point out, but it is a relatively modern aspect in terms of the very long and ancestral history of storytelling. Creating a narrative through sequential conversations was a tool that was kept solely in literature until 1927, when the first feature-length “talking picture” came out. Before that the silver screen was dominated by the bombastic and lively performances of the silent stars with spoken word being saved for those times when it was absolutely necessary for the story.
The narrative came through by the visual events and the emotion was far from absent for a lack of conversation. It would be beaming across the screen from the actor’s actions and expressions. It was a form of entertainment that, when well executed, was almost universally enjoyable without any hindrance of language.
ATR: They still used sound, via piano accompaniment to provide 'atmosphere'..