I say “recently” in a relative way, more so countries that have split in the last century. Places like North and South Korea, Taiwan and China, former USSR states, etc.
Has enough time passed that these countries separated have major changes in their languages yet?
With my limited German knowledge, They are pretty liberal regarding local dialect. People do not speak the same language in Cologne, Stuttgart, or Munich, and at least as a foreign-speaker, it’s not because you understand the people in Stuttgart that you understand the one in Kȯln. Let alone Switzerland. So I am not surprised that German spoken in east-germany sounds different.