I can’t use the “й” character on any folder names.
When I try to upload files from the web UI it doesn’t work. When I try to directly rename a folder using “й” that is already inside nextcloud it doesn’t allow the rename and falls back to the old folder name!
This is not only russian it is a problem with Cyrillic itself. I am using a Bulgarian keyboard layout.
I can not confirm this in general…
In my tests it was possible to sync files from Windows PC to the cloud and rename the file using web UI and will reflect file renaming on the desktop:
Please link relevant topics if you find them already 
according to my charmap it’s a different character (U+0439 and U+0419)…
you need to perform more tests and provide more details.
It’s a strange issue that appears only with the character U+0306 in files’ name.
As far as I understand Russian letter Й \ й can be represented either by a single unicode character which you mentioned (U0439 \ U0419) or by combining a letter И \ и ( with unicode U438 \ U0418) with the specified charecter U0306 wich looks like this: "̆" U+0306: Combining Breve (Unicode Character).
It’s must be pretty rare case, because you can’t simply type this character using keyboard, but for some reason I’m finding a lot of files with it in their names in our corporate doc flow app.
And yes - uploading works via web, but fails in windows client.
yes it is true combined u0418+u0306 provides visually the same result…
and in my system it works as well (as long copy/paste didn’t trick me somehow). the combined character exist at least in char-map - the representation changes depending on following characters but I don’t know a way to translate the effectively used characters…
I created a combined character using charmap and used to rename the file using Web and Win desktop client - both directions worked and was reflected “on the other side”
I didn’t manage to reproduce that again. Maybe I got confused the first time or maybe copy pasting somehow tricked me.
Also the “й” on my Bulgarian layout is only, no matter what you put before or after it:
“й cyrillic small letter short i 02071 1081 0x439 й”
