Proftpd server: Server does not support non-ASCII characters

I have moved my FTP (running proftpd) server from Ubuntu 18.04 to Ubuntu 20.04 server and now there is a problem when connecting to it. In connection log there is a line that says:

"Status: Server does not support non-ASCII characters."

and all files and folders that have non-ASCII characters cannot be downloaded.

I can fix this client-site by setting my FTP client (FileZilla for example) to explicitly use UTF-8 but the problem will still be there for others who connect to the FTP.

proftpd-basic/focal,now 1.3.6c-2 amd64 [installed,automatic]
proftpd-doc/focal,now 1.3.6c-2 all [installed,automatic]
proftpd-mod-mysql/focal,now 1.3.6c-2 amd64 [installed]

Does anyone know what may be that cause for this error and how it can be fixed?

Ok, I have found the solution to this problem!

MultilineRFC2228 off

bellow is part of the documentation about mod_core:

Question: When I connect to ProFTPD using FileZilla, I see FileZilla log the following warning:

Status: Server does not support non-ASCII characters. even though I used the --enable-nls build option, and my ProFTPD supports UTF8. What is wrong?

Answer: FileZilla parses the FEAT response to determine whether the FTP server supports the UTF-8 encoding. However, the format of the FEAT response can confuse FileZilla's detection code. For example, if your proftpd.conf uses:

MultilineRFC2228 on

this causes ProFTPD's FEAT response format to be different than FileZilla expects, which can lead to the above "does not support non-ASCII characters" message.

The solution is to use:

MultilineRFC2228 off

in your proftpd.conf (or simply remove that directive entirely).