No nimbus for Mathematica

We had Mathematica 6 (6.0.1 to be specific) installed on a Debian 4.1 (Lenny/Testing). After setting up an xfs X font server and adding Mathematica's fonts everything seemed to work just fine. But then I remembered that I needed to add the FontPath to the VNCserver scripts. And when I tried to run Mathematica it greeted me with a nice beep and Help → Why the Beep? told me

Unable to find font family Nimbus Sans L with requested face
(weight Plain, slant Plain). Substituting closest match.

Well, I hope that if anyone else gets the same message they can find my solution. Because when I searched the web I didn't find a bit. It took me more than an hour to cure this.

I first thought that some fonts were missing but this did not quieten Mathematica. After much reading and nearly getting lost in trial and error I found a (wrong) hint in an old documentation for Mathematica 4.2. Anyway, this hint pointed me to the file
/usr/local/Mathematica/6.0/SystemFiles/FrontEnd/TextResources/X/Specific.tr

So, by chance, there I found the entry for

@@resource NormalFontWeights
{ "medium", "normal", "light", "book"}

and I remembered from the fc-list output of

fc-list | grep -i "nimbus sans"

that there was no "normal" or "medium". There was only "regular". Thus, adding "regular" to the list of NormalFontWeights as in

@@resource NormalFontWeights
{ "regular", "medium", "normal", "light", "book"}

fixed the problem :-)

Bad nimbus

Maybe I should add that when I tested some more configurations I once was facing the following error message which is – strangely enough – very similar though I was only starting the same Mathematica just by means of ssh -X within the VNC server of another machine:

Unable to find font with family Nimbus Sans L, weight Plain,
slant Plain, and size 10.

In this case fc-list | grep -i "nimbus sans" still showed the same hits but

xlsfonts | grep -i nimbus

was empty because the FontPath for the VNCserver session was not set.