The text is using some character set that your editor or viewer isn't. For example, the text is using ISO-8859-1, and your viewer is using Codepage 850--or vice versa. You can see the plain ASCII characters, but non-ASCII characters like accented letters display as nonsense.
Look at the top of the file for a clue to the character set encoding: if it's there, it may help you to find which editor, or font, or viewer you should be using.