This sounds like an encoding-decoding problem. You can try this.
Rename a copy of the downloaded file to somename.txt. Open the .txt file from within Excel, not from a file manager. This will bring up the text import wizard. On the first page of the wizard, there is a dropdown box labeled "File origin:". Change the setting to "65001: Unicode (UTF-8)". That setting may be a long way down the list. You also have to set the file type to "Delimited". Click "Next".
On the second page of the wizard, check "Comma", then click "Finish". With luck, the file will open without the text corruptions.
You can open csv files with Notepad but there may be a maximum limit to the file size. From the File >> Open menu in Notepad, you can change the encoding from "ANSI" to "UNICODE" (actually UTF-16LE) to "UNICODE big endian" (UTF-16BE) to "UTF-8". The default Excel encoding is UTF-16LE; the Internet usually uses UTF-8.