bad filenames with diacritics?

[GoodKnight]

Received a series of filenames with diacritics in them. FC sometimes recognises them. Sometimes not: and then I dont know what they are because FC interprets them into something else but weird.
Now for these files FC doesnt recognise the filetype and I cannot rename them, because if I try that through F7, change the name and <enter>, then I get error message "file not found".
MS Windows Explorer actually can read the files, with some funny characters though.
Presume it's something with coding, but cannot find anything in the Settings of FC around which coding to use.
Any suggestions how to deal with this in FC?