Since a long time ago.
There are parts of Russia which are perfectly reasonable to be labeled as homogeneous. They form the majority of Old Russia. In fact, pretty much everything bar Moscow, St Petersburg and to some extent Smolensk.
Either way, it would work in Russia since most of these non-Russian ethnic groups are reasonably well integrated, much more than blacks in the US.
Just like it would work in Canada had it been 100% English-Canadian and Quebecois.
Central European is not an ethnicity.
They are ethnically diverse in that they are Swiss Germans, Swiss French, Swiss Italians, Swiss Walsers, Swiss Romansh and it can be argued that due to centuries of isolated mixing and cultural integration, they are pretty much one ethnicity. In the same way that some argue there are no longer any discernible differences between the majority of Occitan people and Frenchmen... due to centuries of isolated mixing and cultural integration between the two, be it forced or voluntary.
Then give an example.
Stating it as a fact isn't a fact.
Customs are virtually the same. Purpose is the same. Traditions are the same. History is the same.