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?
My parents emigrated in the late 1950s. After the Berlin Wall came down, they returned to Germany as tourists and noticed that former East Germans spoke a noticeably different dialect to West Germans, my father said it was similar to the difference between British English and North American English, but the change had come in only about 30 years.
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.
It is true that here in Germany Eastern and Western accents differ, however, also in between the Western or in between the Eastern accents you have quite some difference.
On the other hand I would also say that most Eastern accents share a common undertone, more so than the Western ones.