Guidelines for the form to the left:
First select one of the controlled vocabularies (CV). Then the form fills the dropdown with the languages which are available for the selected CV. Finally press the Show button and the diagram is shown below - large CVs may take a few moments.

Guidelines for the diagram, below to the left:
When the CV was loaded its virtual root is shown in the centre of the dark area, to the right of it a maximum of two levels of a hierarchical taxonomy tree.
Clicking on a CV term moves it to the centre and expands lower levels.
If a list of terms exceeds the display area: move the cursor into it, keep the left mouse button pressed down and drag the whole diagram to a position that shows the missed terms.
Label with red background: narrower terms exist (click on it). Label with grey background: no narrower term exists.