Hey guys. I downloaded the actual WPI, and in fact, the Manual shows up. But always the english one is showing up.

I played with your function in main.js and got it working I hope. First I changed the syntax at FileExists, file:// isn't necessary I think. And I added an else in there, because otherwise it gives an "undefined".

CODE
function SetupManual()
{
position="main.js";
whatfunc="SetupManual()";
var tmpLang;
if (!FileExists(""+wpipath+"/Manual/"+Language+"/index.html"))
tmpLang="en";
else
tmpLang=Language;
document.getElementById("layermanual").innerHTML='<a href="file://'+wpipath+'/Manual/'+tmpLang+'/index.html" target="_blank"><img id="OpenManualButton" src="./Themes/Windows/spaced.gif"></a>';
}
P.S.: I am a noob in programming, so it could be that there is a better way?

EDIT: Another thing that I just saw: If you go to the config page and add a new entry (or edit an existing one) and select "Other" as category, there is no new text box to enter the new categories name. The manual (that I am translating atm) says, there would be such a box.