I created a few custom aspects and added display-label attributes in the web-client-config-custom.xml. This works ok and I see the labels on the details page of the document. But I also have added them to the advanced search page, but there the display-label is not used. I cannot seem to find a away to translate the label of an aspect on the advanced search page.
I can't believe that no-one has never added aspects to the advanced search screen and did not need to translate them. Anyhow, a work around naturally is to use aspect names that need to translation, so that is what I did "Bedrijf" instead of "company". But it's not how it is supposed to be.