Written language pulls together what spoken language splits apart.
For probably the first time in history languages are no longer dividing and multiplying and declaring independence at the same time that more and more nations are. Go figure. Dialects are disappearing under the onslaught of mass media and standardized education, in favor of a national standard language. A language is a dialect with a book and a sword. National languages are themselves in danger of disappearing in favor of international standards, once the national languages become deviant or pidginized to the point of incomprehensibility. Already French and Chinese movies offer subtitles in their own language. IN THEIR OWN LANGUAGE! This is understandable with mutually unintelligible Chinese dialects that share the same written language, but French has no convenient excuse. It’s just hard to understand in the vernacular, like subtitles for senile mumblers in documentaries.