Ok, I’ve got my own tricky solution. Localization file replacement. TSCalculationEngine.strings is responsible for Numbers.app calculation mechanism localization. You can replace it with english version.
Open Terminal.app and run following:
cd /Applications/Numbers.app/ # Where is you Numbers.app located?
cd Contents/Resources/
cd ru.lproj # Your localization path
ln -F -s ../en.lproj/TSCalculationEngine.strings .
Wuala! You’ve got English formulas in a Russian Numbers.app. You have to redo it after application update I guess.