Java properyfiles are encoded in iso-8859-1. this standard does not support special characters. but there is an escaping mechanism to use unicode characters (utf-8) in this propertyfiles.
An excample of a french propertyfile:
To make a proper file you can save your native textfile with utf-8 and then transform it into this special java-format. You can use therfore the java tool native2ascii.
native2ascii -encoding UTF-8 messages_fr.txt messages_fr.properties
To get a utf-8 file out of a propertyfile you will use:
native2ascii -reverse -encoding UTF-8 messages_fr.properties messages_fr.txt
If you are not able to do it (maybe you are not a developer or you have not installed java sdk) we will do it for you.