Predictive input doesn’t work on Russian language
DFU restore to iOS 12, than to iOS 11.4 solves problem.

How to do DFU restore: https://help.ifixit.com/article/108-dfu-restore

If you want to install custom downloaded version of iOS (that must be signed by Apple) click "Restore" in iTunes with pressed Alt/Option key (Shift on a PC). Then window with selection of .ipsw file will be appear.