I'm gonna give my 2 cents on the topic:

Design critique

• The current version (blue link preceded with right or down arrow) is, I believe, very inconsistent with any other user interface. I think the solution should aim at changing that too.
• Introducing a line below the text does not make it more intuitive to me. I'd rather avoid the line and add a left margin to the table to display some hierarchy.
• The accordion-element-like option does not make it more intuitive either. In fact, I think it makes the table more confusing (there is now another header row to the table, although not helping the rows and columns definition) and makes the presentation more cluttered in general.

Suggestion

• If possible, I think I would like to see something similar as the collapsible sections in MobileFrontend (minerva skin)

Side note

• For the record there is also this option Manual:Collapsible_elements, but I can't see it as an interesting solution (imho, doesn't look very good and wouldn't fit well in the UI).

After the weekly engineering meeting we decided the following:

• Expand-link
  • We start with the adding a line below the link-option (border bottom and changing the width of the link to the width of the expanded term box
  • Later we may add a full box around it instead of just a line
• "configure"
  • Keep with "In more languages" link
  • Change the wording to "configuration help"
• "All Languages"
  • we draw a box around the bottom "All languages link". Its top border collapses with the bottom border of the term box.
  • "All languages" gets a little blue arrow

Revision Slider has also an accordion (T145934), so has advanced search (T101087)