Hoi
u sprekt duits? You speek german? if so, I´d forward german translations to you and you can translate it to dutch.
but it is even possible to do it from english.
Some things to remember:
only translating the *ini-Files is at least not enough. as a little bug, frontpage items and also some admin-items will be filled with entries from a file called english.php in com.../joomdoc/views/themes/default/language.
So this one has to be translated, all the files in /Language and administrator/language relationg to Joomdoc, then you will get the effect.
also important: all has to be encoded in UTF8, NOT Ansi or Asci...best way to do is to edit it by something like notepad ++
if you are interested, let me know
best regards
groetjes
uliwak