What is 1/4 ст кукурузного крахмала in english?
It is not a tablespoon, this would mean that 1) they missed an important part of the abbreviation (it should have been ст. л.) and 2) they are directing you to use 2.5 grams of starch. This is a tiny amount which has few possible uses in a tart. Also, since Russians don't use the Imperial system, they don't have measuring spoons graded in "1/4 tablespoon", so if it were tablespoons, the recipe would require the baker to visually judge when his eating spoon is 1/4 full. It is not impossible, but very rare. 

My guess is that they mean "стакан", which translates to "glass" - the one of which you drink, not the material as such. So you need to use a quarter of a drinking glass, which falls in a much more reasonable range. Of course, there is the problem of finding out exactly how much to use. 

Russia does not use the Imperial system, so all volumetric measurements are done with whatever actual crockery you have lying around the house. You can see more discussion in this question. Your choices are: 


Use the size of the glass sold by the Soviet manufacturing plants years ago, but a green tea tart recipe is unlikely to have existed in Soviet times. 
Interpret it as 1/4 cup. Some translations use "cup", but I suspect that the people who translate them are not aware that this is a standardized unit of measurement as opposed to the physical item. But if you suspect that the recipe has been translated to Russian from a Western source, this becomes a very good bet. 
Third, you can wing it, since it is a very inexact measurement anyway, and use anything that falls in the range (from 150 to 300 ml per glass), that's 25 to 50 g for your 1/4 ст. Then you have to adjust your recipe by trial and error. 
Lastly, you can look at the role of starch in the recipe and calibrate it using standard ratios. Here you will also see if it is not some other measurement (tablespoons) after all! 


If you say now "this is too complicated, I only wanted the right amount to use" - sorry, the recipe just doesn't say it. Most people who think that measuring in glasses is simple just don't realize that it is an unreliable measurement.