I've found the solution
My locales didn't apply to the user tomcat, who's running my tomcat5.
tomcats language was set zu en_US, therefore the ASCII.
Another way to get around the problem would be, to update to java 188.8.131.52 and set
-Dfile.encoding in /usr/share/tomcat/bin/catalina.sh
(java 1.4.2 has a problem with Dfile.encoding)