Is it possible that West and East Germany decide to develop their own languages? Maybe East Germany, in order to develop a seperate East German identity, decide to implement some German dialect as an official language, like Low German.
This has happened in other countries, such as Moldova and Romania, where Moldovan is technically just like Romanian, but has been renamed Moldovan for the sake of national identity.
AFAIK, both West and East Germany always had the goal of in the end uniting, thus there was no concious effort in either country to develop a seperate culture from each other, but I might be wrong?