Characters can be misinterpreted mostly if CotEditor fails to detect the documents’s text encoding correctly. There are several things you can try to solve the problem.
The document may appear correctly if you open it using a different text encoding.
Adjusting the priority of encoding detection may help reduce garbled text.
If you select “Refer to encoding declaration in document” in Format settings, in-document encoding declarations, such as “encoding=” or “@charset” take priority when CotEditor detects the text encoding.
If a document can’t be interpreted as plain text, such as binary data, CotEditor can’t read the content text. Open the document in an app that supports its file type.