The bug

The mode ("Load", "Corner", "Save") and the mirror ("|", "← →", "↑ ↓") button of the structure block edit GUI have narration text which cannot be translated.

Background:
20w46a added the GUI element class CycleButton (Mojang name) which has a description text component. In previous versions regular buttons were used for the mode and mirroring, which had initially the placeholder "MODE" and "MIRROR" which were however overwritten during initalization of the GUI so the user never saw them and they were not narrated.
When switching to using CycleButton it appears it was missed replacing theses hardcoded "MODE" and "MIRROR" texts.
For the buttons of the command block GUI translated narration text is used, as expected (see new translation strings with prefix adv.).

How to reproduce

1. Enable the narrator in the accessibility options
2. Change the language other than English (does not work in 1.17 snapshots yet)
3. Place a structure block and right click it
4. Click on the mode button (bottom left, having the text "Load")
   The narrator reads "mode translated mode type" ("mode" is not translated)