See issue 23494 analysis (bug was closed in
that category) - here is description from it

I'm testing FFJ 4.0 FCS RC2.

I'm running in ja locale on a pseudo localized
ffj that has the help files and javahelp control
files pseudo localized to emulate real
localization.

This process has been going on for some time.

so a given pseudo localized help file will
have all the help files in docs/ja except for
the _ja.hs file in docs.

And the xx_ja.jar localized file lives in
modules/docs

1. Given this setup, invoking help->contents,
get the exception message about help and the
terminal output about the tomcat-idx.xml illegal
character.
(ide.log attached)

Specifically, thesea. 
Parsing failed for
nbdocs:/org/netbeans/modules/tomcat/tomcat40/do
cs/ja/tomcat-idx.xml
Exception caught while parsing
nbdocs:/org/netbeans/modules/tomcat
/tomcat40/docs/ja/tomcat-idx.xmljava.io.CharConversionException:
I
llegal XML character 0xa4

b. 
ava.lang.NullPointerException:<no
message>java.lang.NullPointerException
[catch] at
org.netbeans.core.JavaHelp.displayInJHelp(JavaHelp.java
:598at
org.netbeans.core.JavaHelp.showHelp(JavaHelp.java:274)at
org.netbeans.core.Help$HelpCtxProcessor$Presenter.actionPerformed(
Help
...... (see ide.log)


And the help viewer appears empty.

2. help->help contents does show the chosen
help set (except the tomcat one)

3. context help (like help button on file->new
wizard, just for ex
ample, shows empty
help viewer, with same exception/terminal
messages.


4. Attached tomcat-idx.xml has just
one<indexitem text="XXtext"with
multibyte just to show that any
multibyte in this file at usual 
location where localization happens
causes the problem.

5. if no multibyte is in localized idx.xml,
then all works ok.

===> other bug points out some errors in
xml of this file - I removed the empty first
line, repseudo localized the file and all works
ok, so the fix could be removing the empty
line; I don't know if the other xml issues
in 23494 need to be addressed