HI Mikhail
So if I understand correctly, you want to have a Russian language message in the "Join Time-out Message" in the chat widget.
In 10.6 this is supported via the CCX App Admin "Chat Web Form Configuration" page itself. Just need to provide the Russian text in the text box. Tried this just now.
The API should also accept the Russian text.
If you are facing any issue, then please open a TAC case with the CCX product.
Regards