A couple things that can't possibly work - the copy constructor checks if the
arguments field is null, and if so, does not copy the arguments from the string
that is being copied.  It will always be null - it should be checking the value
from the passed JavaI18nString.

    protected String[] arguments;
    protected JavaI18nString(JavaI18nString copy) {
        super(copy);
        if (arguments == null) return;
        this.arguments = (String[]) copy.arguments.clone();
    }


Also, become does not actually override I18nString.become, because the argument
type is different:
    
    public void become(JavaI18nString i18nString) {
        super.become(i18nString);
        
        JavaI18nString peer = (JavaI18nString) i18nString;
        this.setArguments(peer.arguments);
    }