From when I have installed joomfish the field "terms and conditions" don't work,
in back-end the text it is written correctly but in front-end the popup is white.
Hello. I'm assuming that you don't have the latest build of DT Register because we recently fixed some JoomFish issues. Download it from My Orders, then reinstall. The latest will show as 2.6.7e in the installed components area. Also, reload the DT Register Config content element file for Joomfish.
After reinstalling, re-save the config of DT Register. Then redo the translation of the config file. Once it is re-done, you should be just fine.