Since I have only access to Latin1 it is hard to fix this issue myself. The core of this issue is that the guest or user with a different charset will run into this issue. The only way to circumvent this right now is to switch the user language to RU.
I already added a precaution measure when you want rename a page with the wrong user charset you will get a warning and an error message.
In most deployments this is not an issue because they use only one or the other charset.