When inserting a link to an existing wiki page or external link, the display text (= label) in the resulting link is forced as the plain technical string of the page or file, including the namespace etc. For external links on mediawiki.org it is shown as "[1]". Changing the link display text (= label) is only possible in a separate steps afterwards. For pages, after saving the link (closing the linking dialog box), it is possible to go into the middle of the current display text (= label), type the correct display text and delete the originally inserted text before and after the corrected text (which is awkward). For external links, displayed as "[1]" I have not managed to change the display text in this way. However, when (and only when) opening the link a SECOND time for editing, a button "add label" appears, allowing to do this. After now showing the full URI, it is again, as above, possible to correct the display text.
SUGGESTION: In linking dialog, always support a second text field for the display text/linking information, both when creating a link and when editing it. Compare how easily and intuitively this is handled in Google docs.