WinCC provides you with the option of exporting configured texts into text files. You can then translate the exported texts into other languages and import them into the WinCC project. To process the texts you should use a text editor that saves the texts in the Unicode format. In this way the texts can be imported into WinCC without corruption.
For example, you can use the "Notepad++" program (shareware) to save Cyrillic texts in Unicode format (UTF).