The Forest of Time
The Forest of Time is an alternate history novella by science-fiction writer Michael Flynn. It was originally published in the June 1987 issue of Analog magazine. In 1988, the story was nominated for the Hugo Award for Best Novella.
It takes place in an alternative world where the Thirteen Colonies, after getting independent of Britain, did not succeed in creating the United States but developed into separate and mutually hostile nation-states which often fight bitter wars with each other.
The plot takes place in a Pennsylvania whose inhabitants speak a language which they call "Pennsylvanisch" and which a character describes as "[a] German dialect mainly derived from Swabian and with many English loan words, which a speaker of High German would find it difficult to follow".
This language has a rich literature of which the Pennsylvanians are proud and they feel suspicious of and threatened by the hostile English-speaking nations of New York to their north and Virginia to their south.
In that Pennsylvania, it is only the Quaker communities who still speak English as their native language, and are therefore recruited by the Pennsylvanian Intelligence Service as spies to be infiltrated into the territory of the neighboring nations.
In actual US history, a large part of Pennsylvania's population in the 18th century were indeed German-speakers, though the elites in the colony and later state were English-speaking. The numbers of German speakers dwindled in later periods, though the language still survives, especially among the Amish. It is known as "Pennsylvania Dutch" ("Dutch" here meaning "German" rather than referring to the Netherlands) and sometimes also called "Pennsylvanisch" by its own speakers.
Flynn assumes that in a situation where Pennsylvania became an independent nation-state, distinct from and often fighting with its neighbors, Pennsylvanisch would have had a chance to become the official and dominant language, which later immigrants would learn upon arrival.