[Tainan]

Not really very surprising. Many immigrant groups tend to dissolve after a number of years pass.
The U.S.A. is full of such areas and communities that once were enclaves of non-English speaking immigrants that are now remembered only by neighborhood and street names and buildings that once reflected the heritage of the immigrants.
All things pass.

[Cossak]

All Kirghizian industry was built on USSR budget money and was part of USSR economy. After dissolving USSR their economy collapsed local nationals became hostile and Russian-speaking folks moved to other places. Just like in other post-USSR Stans