The Russian Toy is so similar to the longhair chihuahua that it seems unlikely they are not directly related, and are often considered together. The smoothcoat Russian Toy often looks like a miniature pincher. The longhair is in most cases truly indistinguishable from a chihuahua, although the best longhair specimens have the breed-unique trait of very long hair dangling from their upright ears.
Some Russian breeders claim (perhaps only from chauvenism) that the Russian toy predates the longhair chihuahua in their country, the latter "officially" introduced in the late 1950s. But it's wildly improbable a dog already centuries introduced into Europe would be unknown in Russa. Others speculate it originated among Russian breeders attempting to reproduce the papillon without having papillons to breed, and it's the distinct product of multiple toy breeds, chihuahua included.
It hasn't become terribly popular in North America because it lacks sufficient characteristics to distinguish it from the well-popularized chi. But it's such a pretty thing in its own right I have to suppose it will be making further inroads in America.
Shown above are four out of a great many books in Russian about the breed: 1) Russian Toy Terrier by V. I. Kruk. 2) Russian Toy: History, Standard, Maintenance and Care by B. B. Shapovalov. 3) Russian Toy by E. B. Tsygankova and N. V. Lanco. 4) Russian Toy: Maintenance and Care by B. B. Shapovalov.