I am also having this issue.
Is this an issue with this version or has it always been 95% Russian 5% English with the English option selected?
After further investigation it appears the Translation is based on an older version of the game.
I extracted all the game files from the game itself to take a look at the games dialogue and the translation to see what was wrong. With no knowledge of how Ren'Py works i can just make a few assumptions.
Ren'Py Translations appear to take original text and hook them to lines of code within the game.
For example :
# game/my_events.rpy:263
translate English _call_music_for_scene_5c7ffb15:
# C "(Да, да, просто попробуй.)"
C "(Yep. Just swallow it.)"
Seems to refer to line
263 in the games event coding. It replace the original language dialogue and replaces it with (in this instance) the English.
The issue seems to be its an old translation and the Dev added lines of code which makes all the numbers incorrect.
Line 263 in the above example is now line 304, so the translation is not working.
So in order for the translation to work again each line has to be pointed to the correct line now that additional content was added.
As a test run I replaced lines of dialogue in the code and the translation lines and it did work. So it now comes down to replacing all the lines with the correct ones for what appears to be 8000 lines of dialogue ( 31,000 lines of event code of which approximately 30-40% seems to be the dialogue).
While not necessarily difficult, it is a very time consuming matching game. Someone may as well replace the Russian lines in the original dialogue with English to ensure no lines of code are missed, and re-upload a fan translation.
As I said I've never looked into Ren'Py before, and am just using some old Programming knowledge (Pascal was the last coding language I tried to Code anything in) and logic, but if im wrong let me know if there is an easy fix that i missed...
That being said, with the dialogue in hand and a little effort this game has been fantastic. I would reccomend people trying it, as it is a great game so far.