Try the following ways:
1- on the “Edit Current” check if the format of the text is “MIME” or “Notes Editor ” then change it to either one and then try .
2- on the “File” ==> “Preferences” check if the emails editor is ” Word” or “notepad” then again change it to either one .
3- when you receive an email right-click it and then check what is defined over there the Encoding is it “European” or what
4- If non of the above suggested answers worked uninstall LN client and reinstall it .