[Groff] Hyphenation in German

[Ulf Bro]

Hello,

I seem not to be able to include a hyphenation file such that it works 
properly.

I have used the dehyphn.tex file, even removed all the stuff that isn't 
interesting for groff, even changed all letters to latin-1, but whatever I 
try it doesn't hyphenate words with umlauts in them.

Can you point me to the appropriate documentation of how to hyphenate German 
Groff (gtroff) documents.

Ulf