At which URL did you encounter the problem?

An example can be see at https://skosmos.ub.rub.de/diga/en/page/1512826464.

What steps will reproduce the problem?

1. Hover over the 🛈 symbol in the page heading (preferred term) and the term in other languages (abaco).

What is the expected output? What do you see instead?

For the preferred term, the label property dc:source is correctly displayed in a popup. For the term in Italian, the popup appears, but is empty.

What browser did you use? (eg. Firefox, Chrome, Safari, Internet explorer)

Firefox 95 on Ubuntu 20.04.