I've made a Dutch translation for the [url=http://www.oosterkerkhaarlem.nl/SS-forumfiles/DOM_nl_NL.zip]DataObject_Manager[/url].
I also removed some typo's from and added the right filename to the Dutch translationfile of the [url=http://www.oosterkerkhaarlem.nl/SS-forumfiles/IG_nl_NL.zip]ImageGallery[/url].
BTW The "Add images to..." button on the Photos tab of the Image Gallery isn't completely translatable. The tag for 'to' is missing. I know you already have one in the DOM-language-file: $lang['nl_NL']['DataObjectManager']['TO'] = 'tot';. But unfortunatly it can't be reused. The 'to' on the button should (in dutch) be translated as 'aan' instead of 'tot'.