This can be tricky simply changing the "advertised" encoding does not make up for the fact that there are bytes in the file that cannot be understood using a UTF-8 interpretation. In Ant you will need to update the javac
task to add an encoding like, <javac ... encoding="utf-8">
Make sure that the file encoding in Eclipse is also UTF-8 because some cp1252 characters do not directly map into UTF-8 either. You will probably want to maintain your entire project using a single encoding. Otherwise the compiler will be seeing different encodings when it only expects one.