Most of the time when Java files have !ascii characters they don't 
specify the used encoding in build.xml (usually ISO-8859-1) and 
javac/javadoc split out warnings about this (Many Gentoo machines are 
probably running with UTF8 locales). For this reason you can add 
JAVA_ANT_ENCODING="ISO-8859-1" to the ebuild and with the latest 
javatoolkit the build.xml will get modified to specify the proper encoding.

Regards,
Petteri