Hi Harald, thank you so much for your fast reply! Your solution definitely helped, but it is not completely working yet. I can now save the HTML, which is great. However it only saves the translation when I first empty the textarea and save it, whereafter I give the translation and save it again.
So when I load the previously translated item and I try to save the changes, it doesn't save. I need to make the textarea empty first and save it.
Do you have any idea, why it doesn't update the content, except when there was not content? The translated item itself is not deleted though, because the title is also translated.
PS I now added the same xml to the admin component directory of the Advanced Module Manager and called it jdiction.xml to make it a bit more neat and update proof.