Hi,
Yes, my WordPress installation is in my language (dutch).
After trying some things I figured out what the problem was, renamed the mo- and po-files (poedit just called them nl_NL.mo and nl_NL.po, after renaming they have comment-mail- as a prefix) and moved them to wp-content/languages/plugins.
Those actions where the right thing to do so my frontend is now in Dutch.
Thanks!
Henny Struik