Simply Incredible!

Chunky white letters, amazing character set.

There is a big difference in size between the capitals and the lower case, which brings many problems. The numbers are too small for a text set in capitals. Likewise, the special characters, diacritical marks would not survive in an all capitals setting. Actually, you had to create a larger set of diacritical marks for the large caps. To solve this problem, I would suggest to put those big capitals in a separate font as initials. (initial = a distinguished initial letter of a chapter or section of a document, often illuminated, decorated)

This font is not monospace, but it has a tendency toward uniform width. As a result, we see the M,W to be very feeble and anemic. To preserve the same width, try a blocky M,W, with not so deep incisures, much like your Russian "Ш". However, I can see the added charm with strokes of variable width. I also understand the design concept of putting the letters next to each other without gaps, like slabs of white stone.

Speaking about the Cyrillic set, the glyphs are very nice and consistent, with a few minor anomalies. Those, I would not mention here, because such small deviations may fall into the category of broad stylistic freedom a designer always can afford. So I resort to the other issues: "Д" has a descender, sort of. Since you already have some descenders among the Russian caps, I don't see any problem having one more. This letter is a strong character in the Cyrillic alphabet, often serves as initial in Russian text; thus I would make it a bit more robust. The Cyrillic Э,З, and number 3 are too similar. The Cyrillic "м" is not equivalent to the Latin "m". In fact, the latter glyph (m) has a place in the Cyrillic alphabet, mostly in cursive form, as the equivalent of the Latin "t".

Please, note that I only comment on those alphabets I can read and write. There may be other issues I can not recognize. This is a major project covering a number of different languages with a plethora of exotic glyphs involved I don't even know the names of. You have the courage and attention to details to undertake such project. With all the critique above I only wanted to help to make your font better.

Obviously, any text set with this typeface in any particular language is aimed at primarily the native speakers; they will be the final judges on legibility matters. It is a bold move to design letters you are not fully familiar with. I can only encourage it. I might add that Fontstruct is a safe learning environment for such endeavors.
(I'm currently studying the Greek alphabet to be able to design some nice Greek fonts some day.)

Congratulations to your work. It still gets my 10/10.