Hi again bangka. If you re-download again my zip file (you may need to clear browser cache to get updated zip), I added the java sources there.
I also modified codes to get Ё and ё as you said, and cleaned to ' ' all unused symbols to save memory. See my fork of esp8266-oled-ssd1306 repository - I added Cyrillic stuff there, too and similar to your mod in OLEDDisplay.cpp. (but not tested yet).