After some comments there I decided to search for the bug and yes I have already found it and reported it in tracker. But nobody answered me and I think it is because it didn't get many votes.
Then I searched again and I found a solution which I proposed in the tracker.
But again nobody looked at it
Maybe there are not enough developers right now or it is not so important.
I wish I could change the code myself but I don't know what exactly is a patch and how to apply it.
The worse thing about it is that we are not allowed to change the text in English. An author/developer of a plug-in told me that maybe moodle or his code needs this backslash so he was afraid to change it. The truth, in my opinion, is that what we see in English strings is not the original string the author wrote. The bug changed the text and we are now afraid to restore it to the original. Instead we have to contact ALL the authors and persuade them that there is a problem and they have to make the change
themselves.