It seems that the character encoding used when serving HTML help files depends
on the web container (and system environment?) serving them.

At the moment, this causes non-english help texts to be displayed mangled in the
GUI.

These were the values for the HTTP header "Content-Type" in my setups:

Jetty/Windows: "text/html", i.e. no encoding specified at all.
Winstone/Windows: "text/html;charset=utf-8"
Winstone/Linux: "text/html;charset=ISO-8859-1"

As all HTML files within the Hudson web application are encoded in UTF-8, I
would suggest to enforce that convention by nailing down the encoding with a
filter in web.xml like the following?

[...snip...]

<filter>
<filter-name>force-encoding-filter</filter-name>
<filter-class>hudson.ResponseHeaderFilter</filter-class>
<init-param>
<param-name>Content-Type</param-name>
<param-value>text/html;charset=utf-8</param-value>
</init-param>
</filter>

<filter-mapping>
<filter-name>force-encoding-filter</filter-name>
<url-pattern>*.html</url-pattern>
</filter-mapping>

[...snap...]

Given an OK, I could change the web.xml accordingly.